Spikes versus Rubber on wood floor?

Whether to couple, decouple and dampen, etc., is determined by experiment. Theory does not help because whether any result is positive or negative depends on a wide range of factors. With a suspended wood floor, coupling will mean that the floor will be able to better act as a resonant sounding board itself. That is good, if you want some bass/midbass warmth, and bad if you want to tighten up the bass.

I personally use a Symposium Svelte shelf under my speakers. This thin, multilayer platform is coupled to the whole bottom surface of the speaker enclosure for effective transfer of vibrational energy to the platform. The inner layer then converts that energy to heat. This is an effective way or reducing the shaking of the speaker itself (generally not a good thing for sonics), and dissipates this energy instead of transferring it to the floor. This tightens up the sound noticeably, which is a good thing in my system.

inpepinnovations - stick around here and you'll find out. Otherwise, just buy the cheapest new stereo you can find and enjoy how well it measures.

If the floor seems to be the offending item, I always recommend fixing the problem, instead of adding some other item into the mix to try to mitigate the floor problem.

Nsgarch has some good advice about locating the speakers over the joists, and there can be supports placed under the joists too.

I had speakers with cones and down firing subs sitting on a suspended floor in a relatively new home. The floor has a resonant frequency of 34 hz, and I know because at that frequency the amplitude of the vibrations increases so much it shakes the chair and tickles my butt!

To solve it, I cross braced the joists, put a post under the center of the floor, and put a piece of slate between the cones and the carpet (isolation). This combination works very well indeed, and there is no visible movement of the speaker tops.

So, my experience and that of Fiddler are very similar, in that we both found isolation was necessary on a suspended floor. That does not mean coupling should never be used, as these same speakers on a concrete floor shine with just the cones.

Obviously even well constructed speakers vibrate or spikes would not work their way right through pennies placed underneath them.
Given all the divergence in answers, I decided to approach this logically through a hypothetical example. Please tell me where you think my reasoning is correct or incorrect. Lets say we place a vibrator on a kitchen table when the kids aren't home. In my example the vibrator is equivant to a speaker.
We turn it on (turn about is fair play). What will it do? It will clatter. This is equivilant of a poorly coupled speaker. Then we press down on it adding weight. Now it is coupled to the table and the table will act as an amplifier of the vibration - rather the disipate, the noise will get louder, true? This would be similar to a coupled speaker interacting with the wood floor. The speaker is now less vibratory but the table is magnifiying the sound.
Next we place an inert substance such as styofoam, sand, or rock between the vibrator and the table. We now get less noise. This suggests to me the best is to firmly couple the speaker to something rigid enough to reduce the speaker's vibration,and under this have something non-resonant so that the vibration is not passed to the floor.