Best treatment for speaker feet????

The cheapest and perhaps sufficient approach would be just to get good big spikes, say, Audiopoints brass spikes. They should penetrate the carpet. Another possibility is 2" thick spiked maple platforms under speakers and spiked speakers. To possibly improve it further - Boston Audio Tuneblocks S for spiked components, that's under spiked speakers between speakers and spiked maple platform. I use them with my speakers.

Well, I use both coupling and decoupling devices together, Polycrystal spikes with Boston Audio tuneblocks for spiked components, on a wooden floor in my appartment. It is better in every respect than just spikes, especially there is less distortion in all frequences and everythings is tigher and sharper. But my speakers are quite loose and do perhaps need more control than average.