My design combines both concepts but doesn't need PoW (formerly I had unprofitable PoW but hence replaced it with something better)! That is a very strong hint for you.
Would you mind telling us more about your discarded idea of unprofitable PoW?
Some time ago, I came up with such a concept myself:
https://bitcointalk.org/index.php?topic=1591011.msg15981017#msg15981017My basic idea was to use PoW as means of "honing" your address/account, so that mining would become more beneficial for low-scale miners than for big players.