sdl4,
Unfortunately you are asking for clarification on the one comparison I feel less sure about.
It's been quite a while since I had spikes under my 2.7s. The 2.7s were second hand and didn't come with spikes. But since I also owned the 3.7s at the same time for quite a while, I had grabbed the spikes and tried them on the 2.7s. But I sold those spikes with the 3.7s years ago now.
Anyway, simply from memory, I don't remember the spikes changing the sound very much (which is a good thing IMO). But it was easier to shift the speakers around on the floor without them, so I didn't keep using them.
But spikes are definitely the case where my memory on this may be less reliable, since I haven't had them for a while.
FWIW: The Herbies big sliders worked really well under my speakers. Didn't "help" the sound in any way I noticed but didn't seem to hinder it much. I took them off recently to try the Townshend bars but haven't bothered to put them back on afterward, so the speakers are just sitting on my floor. Sounding great :-)