I mean no offense, but I feel like what you are asking for is precisely what is wrong with the development of games. Everyone is EXPECTING something for progression. Some kind of reward, incentive, prize...however you call it, people's expectations are clouding the fulfillment of the game itself. Why can't you simply play the game because you enjoy it, not because you have to in order to earn a gold star?
I really hope that didn't sound condescending...though I hope it helps make my point clear.
No offense taken. I don't 'need' a reward so long as the gameplay is compelling enough to keep me playing. But if there are no 'rewards' or improvements upon leveling, then why have a leveling system at all?
Believe me, I'm not the type of person who plays games for 10 minutes and gets bored if there's not a bazillion flashy prizes on the screen every 10 seconds telling me how awesome I am. I grinded out HRs in single player for years just to make one or two cool runewords to play with, and that was reward enough for hundreds of hours of grinding. BUT, 'reward, incentive, prize...progression' is exactly what leveling systems are designed around.
So then is the intent of your OP that they just drop levels all together, or just stop at 30?
Also remember that other things are "unlocked" as you level past 30. Items for instance are known to have level requirements up to 60.
If not a leveling system, then how else do you prevent a brand new character from equipping the best item in the game for that class, like was the problem in original Diablo.