I too have the Diners and Sheraton Optima. I would say the $30 renewal fee is worth the benefit of $1 = 4 clubmiles = 4 ff miles if used at Sheraton.
Mostly I like the fact that (I think I may have written this under another thread) one can use 10K points for a night at their luxury collection hotels, a higher value than 10K airline miles (or 20K if one uses the Diners promotion), in my opinion. Anyone tried to use 10k points at Sheraton?
Ken