@RobN I also have Premium, but mostly for the Portal. I agree that the trial program, which is basically just demos, should be available for any PS Plus subscriber or, honestly, anyone. It’s a really lame “extra value” for Premium subs.
That said, I’ve tried a few trials and can’t think of any games I actually bought because of it. If anything, it saved me a purchase because I realized the game wasn’t for me. I shouldn’t have to be subscribed to the highest tier for that “privilege,” though.