If you get tubes that have been tested for microphonics you don't benefit by using them. There was one answer that I thought said there were sub microphonics but they are clearly not audible, whatever they do I don't know the effect on the tube or sonics.
Coolers are really probably only somewhat useful if your ventilation is insufficient after playing your system for long periods but tubes are and were designed to endure the heat they generate.
All that being said if you buy off ebay there is a good chance that they could be microphonic the simple rubber band damper will work for all but the worst tubes. Those are hopeless because the internal components create a ringing sound with vibration you just can't stop it.
As for heat it is really as important as the length of time you use the tube they wear out the longer you burn them. I am not sure what effect cooling the glass will have on the thermionic plates and filaments, most small input double triodes will outlive you anyway.
That shouldn't deter you from rolling tubes though every tube sounds a little different.
Output tubes will typically die during your use of an amp YMMV. The lifespan and screen voltage, what you set the bias at, seem to have a relationship. That makes buying used output tubes that have not been thoroughly tested for gain and mutual transductance a risky business.
