I would not bother with vibration isolation unless I knew it was a problem. I run tubes that are notoriously microphonic--Western Electric 310a and 310b tubes. I have not had any obvious problems with feedback or other obvious effects of microphonics. I sat in on a session where a builder was choosing parts for a custom amp and a bunch of us listened to different tubes to be used in the build. When we were done with making our choices, the builder noted that we had all chosen the most microphonic of the tubes under consideration. Whether we chose them BECAUSE they were microphonic and we liked the effect, or despite the tubes being microphonic (by chance, or we liked other aspects of the sound), I don't know. I don't bother with vibration control besides putting the gear on decent shelves; for me that is Symposium Ultra shelves.
