Maybe my experience can illuminate the question whether to spike or not. During a long audiophile life I have vacillated between spikes or more pliant shock absorbers (SD-feet from Sweden, the Base Platform from Norway and Valhalla Technology from Denmark). All had their advantages, but the main problem was that they made the speakers wobbly and the sound muddy. So I always returned to spikes. So a few weeks ago I by chance discovered Equarack speaker mounts (from the US). I ordered eight of these and put four under each of my Vienna Acoustics Beethoven Concert Grand speakers. Suddenly everything fell into place: natural, smooth, free flowing music but with tight bass and sharp transients. I can`t recommend them highly enough ( I am certainly not paid by the producer to say this!). So this might be the "final solution"! So try them.
Speaker shock absorbers
From time to time people have posted different methods for mechanically decoupling their speakers from the floor to reduce vibration. Some of these have involved using a ply system of rubber strips and wood strips, which seems reasonable to me. I have looked for suitable sized sections of rubber or even for large sheets to cut up but have been unsuccessful. To those who have used that method -where did you find the material and what thickness of rubber and wood did you use for each layer - finally how many layers did you end up using?