Hi, Netdewt. In general, small-signal and power tubes have equivalent potential for distortion from microphonics and microvibration-induced distortion, also with equivalent potential for improvement. Whether damping small-signal only or power tubes only will provide greater improvement varies from one component to another and among individual tubes. You'd likely get substantial improvement starting with either. You might not realize the full degree of improvement because the undamped tubes will mask the results with distortions. By default though, starting with the small signal tubes is a good choice. Damping instruments improve the sound in general by addressing a myriad of specific problems.
Herbie's AUdio Lab