I agree that upping difficulty doesn't have to have unique rewards (besides maybe badges?) and certainly not unique drops, IOs, anything like that. Nothing that some players would be gated from. Actually, I think since the introduction of merits, CoH has a very positive 'play the way you like' system, and I'd like to see that widened rather than narrowed.
Quantity of the same things, maybe. It happens already with XP and inf, but not merits right now. A taskforce run at +0/x1 has the same merit value as +4/x8.
I actually think the whole reward economy needs a look at, to give merits more direct buying value anyway. But I don't know that territory nearly as well as others do. In many ways, I'm in support of making the character building part of the game easier.