I wouldn't worry about valve springs sitting compressed as this is nothing like what they go through when the engine is running. If this were a problem you would have to take the springs out of your suspension as well. What I would be concerned about is turning the engine over when the cam is "dry". As you know the only
oil the cam lobes get is what is thrown around inside the engine. Turning it over once in awhile without starting is causing a lot of unnecessary wear on the cam, especially a flat tappet cam.
If you not going to drive it, it's best to use good storage methods and let her sleep.