Importance of Good Speaker Stands?

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.