Virtually all vacuum tubes are prone, to some degree, to distortions caused by microphonic vibrations, and some tubes internally generate their own microphonics. This is true whether a component costs $200 or $20,000. Microphonic distortions will vary from one kind of tube to another and according to other factors such as microphonics-induced distortions in capacitors and other electronics, which might "mask" a cleaning-up of tube microphonics. Audio improvements are quite subjective, and what might be a minor improvement to one could be quite major to someone else. Even so, the affects of tube dampers varies hugely; sometimes the improvement is miniscule or barely perceptible, and sometimes very upfront and dramatic.
There is no "end all" product or accessory; everything in an audio system must synergize together to achieve the desired end result. If tube dampers are not the "cat's meow" with your system or not really worth the investment, send them back. It seems likely, however, that if you "think" you hear an improvement, you do. You might consider keeping them as part of an overall vibration-control solution.
Thanks,
Steve Herbelin
Herbie's Audio Lab