I don't know about hot/cold compression tests, but most people do tests wet and dry (with and without oil). This will tell you how much ring wear you have.

If loose spark plugs are really a problem, you could probably use a helicoil or thread replacement type device. The use of a non-conducting tape is not advised, as the thread is used to ground the spark plug, and you have a chance that the tape (not saying you can't thread tape properly) will come off and then fall intothe combustion area.