tweak, do they realy bring improvement?

I absolutely agree with Barry - I don't get anything until I eventually get a clue how it supposed to do what it claims. For me understading adds fun, this is not about money at all. So far I couldn't find clear enough explanation how vibration may affect well designed SS devices... so no isolation platforms nor coupling devices have found their place in my shelfs yet. Cables, spikes under speakers are quite obvious... Power conditioners - the funny thing is that the better designed the power supply of the component, the less effect AC tweaks produce. For some reason I haven't heard about so well designed components yet...
However, all this is not about savings, it's about fun, so I don't see a reason why not to buy and try even if it doesn't work? If it makes fun, consider it working!

Barry, it definitely makes sense, but when we're talking about *solid state* amps, for example, I'm not clear what level of distortion vibration may really cause, taking into account the real in-room resonance frequencies.

As for optical discs, you're right, but mainly due to the fact that CDP design doesn't employ error handling schemes implemented in computers, in simple words re-read instead of interpolate. Average CD-ROM vibrates like crazy, but eventually does read the data error-free, while that vibration perhaps affects a data transfer rate. (I do realize that digital audio is more complicated to read and to transfer then data due to addition of another component: timing).