I think this topic of his is one I agree on, and like mentioned, for the price in question it's a no-brainer. I have tested whether or not my cap retains pressure hours after shutting the engine off.
I just go ahead and swap out the radiator cap every time I change the air filter. IMO it's not even worth the bother of testing it.
SMB-less as of 02/04/2012. Our savings account is richer, but our adventures are poorer.