As with all tweeks results depends on the basic quality of your equipment and your ability to discern differences.
I have used inexpensive tube dampers. They certainly did no harm, but since I use very low noise tubes to begin with I can't honnestly say they did any good either. I can certainly buy into the logic for using them.
My experience with tube coolers is similar - since the tube life of any tube is unpredictible I really have no way of judging whether or not I have gotten extra tube life. I stopped using them some time ago and have really not noticed any difference. Just my experience, YMMV.
I have used inexpensive tube dampers. They certainly did no harm, but since I use very low noise tubes to begin with I can't honnestly say they did any good either. I can certainly buy into the logic for using them.
My experience with tube coolers is similar - since the tube life of any tube is unpredictible I really have no way of judging whether or not I have gotten extra tube life. I stopped using them some time ago and have really not noticed any difference. Just my experience, YMMV.