Herbies Pucks floor spike protectors...

My very heavy speakers came with 3 spikes per speaker....the floor is travertine tiles.  Use or not use? (not for floor protection, but for sound improvement)
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You can't easily get Herbie's products here in the UK so I make do with sorbothane or similar.

However, everything I've read about them seems to make straightforward sense. On a solid floor like yours they may be less effective than say on a suspended floor, but it will still depend largely upon the way your speakers have been constructed. 

I'd say it's well worth a try.   
I use them with my Vandy Treo’s. I use them to protect my wood floors.
I can’t say that they either help or hinder, as I would not put spike marks in my floor.
They also help with moving and adjusting the speaker as they glide easily.
I’d be worried if those spikes could put a chip or make a crack in travertine.
I'd be more concerned with keeping your S/O happy and floor damage.

Years ago, I purchased two dozen of these for less than the cost needed for a pair of speakers.

You might even find something that resembles the Herbies, if you have the patience to wade through the listings.

Speaker/subs,table and CD deck are spiked, so I wasn't about to pay for the audiophool versions.

The description of what the  titanium version is supposed to do, seems a little....
Use Herbie's cone/spike decoupling gliders. They work very well in isolating the speakers so they don't vibrate the floors. I also use them under my rack to isolate from floor borne vibrations. They will also protect your tile.

i have 2 brand new , will save you some money.
I added the Decoupling Gliders in brass a few months back to ride under the 3 spikes per speaker.  I felt that they brought a nice touch fullness in the lower registers without losing musical definition, and the mids up seem a bit clearer, too.  And they make moving my speakers a breeze, so for the money they are a great addition to my TAD CR-1's (which like getting more fullness down there).

I am curious to try the IsoAcoustic's Gaia's for comparison to see if they take these musical qualities further.
as I recall OP has 5a. I have used the Vandersteen spike shoes with five A, 7’s and the amps which are also spiked on both tile and hardwood to good effect. they are machined w felt and fit your cones, reasonable for made in USa, available thru your Vandersteen dealer
You guys will laugh,but I have little carriage bolts from the hardware store screwed in instead of spikes with felt pads on the bottom.Cheapo adjustable gliders:)
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Several good suggestions made by all above. Take a look at all the products for speakers made by IsoAcoustic's in order to get a feel for other ideas. 
 @jtcf bravo !!!! add a nut and you have locking adjustable ! 
I use Herbie's gliders under my Wilson MAXX speakers to be able to move them on a hardwood floor. The use of the gliders did not change the sound at all. If I place my hand on the bottom of the speaker when played loud, I don't feel any vibration whatsoever due to the cabinet material and their weight, so that may be the reason they did not change sound. I really like them and recommend you give them a try; my guess is you won't send them back.
I didn't know Vandersteen made spike shoes.

A quick Google shows they should probably work as good as my Herbie's gliders, though some may disagree.
Some of this stuff can get a bit anal.

I use Herbie’s titanium Cone/Spike Puckies on three sets of speakers. They add a noticeable improvement to the sound quality. Tighter bass with better micro-dynamics. 
In regard to JTCF's post above: I temporally used 8M carriage bolts with my Focal 726-floor standing speakers (two months) while I waited to receive my custom 8M spikes. As soon as I installed the spikes I noticed an immediate improvement with dynamics, sound stage, and bass. I believe you don't know what works until you try it.
I still have some gliders. They didn’t do much for me under equipment rack nor Sound Anchors for my speakers (laminate floor), but they protect the flooring fine :D