I think a engine test stand is a great item for new engines. I am building a kit and have the engine, but the plane is not finished. I get to break in the engine and have it ready for the plane when it is finished. I also don't have to mess with tying down a plane and then cleaning it off during break in. I have seen so many post about engine problems on here that could be resolved quickly if they tried to run it on a stand. It eliminates all of the issues you mentioned that you have to set up in a plane. It will essentially narrow down the problem to the installation in the plane, or the engine itself. Next time you have an engine that is giving you fits, take it out and put it on a stand and see if it acts right. If so, check the installation of tank, lines, etc.

Here is mine I just made because I got tired of not having one.
It will take a .15 to a 2.18



more pics here