Importance of Good Speaker Stands?

I have a pair of decent speaker stands for my Wharfedale pacific evo 8 bookshelf speakers. Stands sit on on hardwood floor with rounded spikes underneath the base. The speakers themselves sit ontop of vibrapods for some sound dampening.

My question is this: I can, but have not filled my stands with steel shots and/or sand like I've read many do. Will this result in a noticable improvement and if so what does it do to the sound? Also, any recomendations on fill material and where to get it?

Stands can make a significant difference, but it will depend upon how resolving both your speakers and the system is, as well as how discriminating you are as to just how much difference it will make, and how much that is worth to you. One warning I'd give you - those vibrapods tend to leave marks on everything you put on them, especially wood and metal. Those marks are nearly impossible to remove. I learned this the hard way. Cheapest fill material is play sand from your local mega-hardware store that has "mom&pop", who used to own the local hardware store down the street, working for minimum wage as greeters. The sand itself is dirt I mean it. Better make sure it doesn't come from China and off-gas some rancid cat-piss smell that melts the tip of your cartridge off. Wait a minute, that's kitty litter filler I'm thinking of. You could probably get some of that Chinese drywall for free and fill your stands with it, but I'd just use the sand. Seriously, filling them can deaden the metallic ringing resonances that may exist and will create a more solid foundation for your speakers with less room to flex. We're talking at levels that we can't exactly measure, but yes, you could potentially hear it. The only way to really find out is to try, which may amount only to a bit of a hassle and sand on your living room floor. If it doesn't work out you've got some nice drainage for a garden bed.

It's late, what can I say. I was very serious about the Vibrapods though.
I would try the fill like Jax2 suggested. With those particular speakers, I would look at your situation from a strict resonance control perspective. So true about the mom&pop example. The cat-piss issue can be rectified by LRTIGB (little round things in glass bottles). They equally work well as stink absorbers as well as quantOnium poopy eliminators.
I have Liedtke stainless steel "Diva Exclusive" stands and have filled them with very fine quartz sand (odorless :-)) from the DIY store. As pointed out by Jax2 and Vandermeulen: dirt cheap and may prove to be a tremendously effective tweak. One word of warning, so you don't have to find out the hard way: don't fill the stands to the rim, it'll kill the sound, 2/3 to 3/4 of their height will probably give you the best results (at least that is what worked best for me).
Jax' warning about vibrapods leaving a residue is accurate. It's also true of other vibration-absorbing pads like the rubber and cork pads. After one bad experience I've always used a layer of plastic wrap on each side of the vibration pad. I have not tested different brands or weights of plastic wrap for their sonic attributes.
Instead of the Vibrapods try Herbie's big fat black dots between the stand and your speakers. Very economical with a generous trial period. As already suggested try filling the stands. How much to fill them and with what is the experimental part. I've had good experiences with a combination of kitty litter and fine lead shot (#8 I think). If I get to a point where I need to fill stands again, I would try the micro bearing fill sold by Star Sound Technologies.
One further addendum to the PlaySand suggestion - You'll want to make sure that the sand itself is moisture-free (and I don't just mean cat piss). Sometimes the sand comes with moisture included at no cost to you, until you fill your steel stands with it and the moisture causes the insides to rust. I've heard of folks pouring it into a few big pots and sticking it in their oven at low-temp for several hours to bake off any moisture in it. Sometimes you'll just luck out and find a source that sells bone-dry play sand and as long as you keep it from your cat you're good to go and won't need to Bake any sand pies. The alternatives are all more expensive, short of kitty litter which is not quite as dense or heavy as sand. Lead shot is available from gun dealers who sell reloading supplies, but you'll have those tiny balls rolling around your floor for the rest of eternity. They can be a bit annoying when you step on one. Also lead is not the best thing to be handling, or for pets or children to have access to. I don't know if they make shot out of lead anymore though. Anyway, that method definitely will add more weight than sand. More expensive still is metallic powders marketed by the likes of StarSound (who make excellent isolation products, btw), which will add more weight still, but will take weight from your wallet. Pick your poison.
Use sand, and bake. I live by the beach, and when I constructed a DIY platform for my TT, I used fine sand from the beach for the interior. Put it in a large bowl, and mix occasionaly to facilitate drying. Easy as pie.
I use Star Sound and Atabits , both of which I am a dealer for. Both work well but as pointed out aren't cheap. But you don't need that much of them, too much will deaden the sound. I use to use lead and these are better. Someone recommended steel blasting shot as a cheaper alternative, I haven't used it; the Atabits are small steel balls and work well so I would think these should also.
Very important they be 'massive' and lead shot filled, but only if you do not have children. I've had three sets, two Chicago the other Studio Tech. They make all the difference. The tops of all of them are spiked, no pads viber stuff. The bottoms are also spiked. The speakers, all ProAc's sing, sing. sing.
The stands being filled with material will make the bass sound firmer and less 'wooly', and may even improve the clarity of the midrange.
My B&W 805s have a thick steel plate on the bottom of the speakers and THAT plate screws tight to the top of the stand. So SOME stand mounted speakers are designed to sound best when not able to vibrate at all in relation to the stand. I have a (less then .5 mm) thick layer of generic Blue tack (trust me it was VERY HARD to get the blue tack that smooth and thin, a LOT of kneading manipulation was involved, and a good rolling pin! but it was worth it!!between the speaker base and the stand top, and the stands filled (to the top, and vibrated before sealing to compact the sand) with stovetop dried playbox sand.
(My dealer asked me it it made the sound "GRAINY" hah ha..)

Also the sound perks up if the stands are solidly (all four spikes with equal contact) on the floor. Adjusting the individual spikes height with washers to make the stand 'solid' and not rock at all when pushed 'hard' diagonally made an additional improvement.
Fo you getting those rounded bottom spikes to have equal floor pressure would be a good improvement. (it would have to be done AFTER you found the ideal location.. or you would be spending all your time trying to balance spike pressure instead of listening to music! (If I had rounded spikes, I would check them for 'equal floor pressure' by using strips of paper. placing a strip of paper under each spike and see how hard it is to slide around under each spike. adjust the spikes with super thin washers (even slips of cut paper with a hole for the screw, the cut off the excess paper around the top of the spike and the spikes screwed in fully and tightly into the base of the stand at all times.) until they all have equal paper tension.
When music is playing I can feel a tiny bit of vibration in the aluminum stand shafts, but none in the speaker itself.
Wow, thanks everyone for your responses. It sounds like it's an worthwhile inexpensive tweak to try. Now, sneaking the sand into the house without my wife finding out will be the tricky part. Truth be told, the vibrapods and cones have made a significant improvement on my CD player and turntable. I did not, however, really notice any difference when placing them between the speaker stand and speakers.

With respect to rounded spikes vs "spiky" spikes (sorry, no other way to describe it), is there an advantage. I figured the spiky spikes were for when your stands were on carpet, and the rounded spikes were for flooring. Elizabeth- I'll give your paper pressure test a try.