I've been going through an evolution in my Reference 3.1 stands.
I started by doing a fair amount of research on what was available, as far as different designs were concerned. I noticed two main styles available, add height or add width.
I decided I wanted both!
I started with some concrete blocks from The Home Depot, I got 4 of them for ~ $5. At first I used 1 under each speaker like so...
I then used two blocks on end to get more height, stacked flat they were less stable than like this...
I noticed that with each increase in height of the stands, from 3.5" to 8" , I got a nice increase in the height of the sound-stage. I then added the MDF stands to add 10.25". The stock stands are bolted to these by putting screws through the top of the stand into the cone mounting points on the bottom of the stock stands. Adding the MDF stands was a big improvement over the concrete, not just in sound-stage height, but in the total size of the sound-stage.
I think this has as much to do with the added stability provided by the added width of the stands as it does to the added height. The stock base of the Speakers is only 8" wide, and the cones are mounted 1" in from each edge, so the effective width of the base is only 6", very good for a sleek looking design, not so good for stability. Adding to the width keeps the speaker more stable, limiting the side to side motion, and that improves the imaging by keeping the source of the sound in one place. Imagine the image below is a driver moving from side to side...
...as it's sending sound waves towards you. The sound doesn't come from the same point because the speaker is moving. Adding lateral stability prevents the speaker from moving, improving the imaging and sound-stage. In my opinion, it's likely that one of the main improvements of the 3.5 is the much wider base. It's also probably one of the big improvements made by the Mapleshade bases.
I plan on painting the stands satin-black, to match the stock stands. Once that is done, I'll reattach the speakers to the stands, fill them with sand, and seal them up. The added mass should make them even more stable than they are now, and give me additional improvements over what I've already achieved.