Little update:
After getting used to the spring footers under the speaker for about a week I had some more observations.
First, aside from the positives I described - speakers "disappearing" more as a sound source, larger, wider, deeper soundstaging, more 3D imaging, seemingly clearer, finer detail...negatives where that the sound had less obvious punch and impact, sounded overall "softer," and the soundstage generally seemed to take a foot or two step back from the speakers.
So last night I took the footers out and I think I prefer without the footers. The sound just became more punchy and all around solid - an aspect I really seek in my hi-fi. It also sounds a bit more rich. Taking out the footers I did take a hit in some of the aspects I mentioned. The speakers didn't "disappear" as much, the soundstage did narrow, less depth, a bit less of that absolute clarity. (Not that the speakers actually don't do great soundstaging on their own - they are actually one of the best I've ever used. It's just that the footers took it to another level).
With the speakers on the springs, decoupled from the floor, the experience became a bit more like an electrostatic - an open, boxless window of sound, but also a bit more ghostly.
Of course I'd love to "get it all." I'm thinking I will still at some point try the Townshend isolation device under the speakers. They are more purpose-built, and also essentially don't raise the speaker at all, where the cheap footers had very thin springs, were quite wobbly, and raised the speaker something like 1 1/4" (I did initially adjust my listening height to compensate, but perhaps changing the height relationship with the bottom of the speaker/woofer and the floor may have influenced the sound too?)