After spiking, you will immediately notice a perceived drop in bass. You will realise after prolonged listening that the bass is not reduced, it is just tighter and more extended with less 'boom' or looseness. Those of you with speakers without spike holes, fret not. There are commercial solutions to this problem, usually in the form of 'stick on spikes' or spike kits which can be attached to your speaker with some drilling. Those who are using stands will have the additional problem of coupling the speaker to the stand.
Some stands have top plates with holes that provide for spikes.
I don't particularly recommend spiking the top plate due to safety reasons. A bit of blu tack is much safer. As for components, coupling appears to have a greater effect on CD players, tube equipment and record players. Spikes and cones then to sharpen and brighten the sound while compliant materials appear to warm and soften the sound. If you don't believe in this or don't want to try some of the expensive hifi cones out there, a plumb line weight works quite well.