playing just for rakeback can seriously impede your development as all-around player. As you know rakeback rates for NLHE even up to $200 NL Full games are less than you will make at $3-6 Full. If you are playing just for rakeback and you dont already play NL you are seriously missing out on some of the best action at Party ie the $100,$200 NL 6MAX games-less so in the full games. If you just look at the rakeback numbers from NL --you would never play in these games.
A very good player playing $100 NL 6MAX will make an hourly earn that will crush the best $3-6 Full or 6MAx player's earn...but if you saw you only got 3-4 cents per 100 from NL vs say 5-6.50 cents for $3-6 you'd never play the game solely thinking about rakeback.

You should play in the games that offer you the best overall earn-sometimes that means playing in games away from Party with no rakeback ,sometimes that means PartyBBJ games w/ no rakeback..play where your overall earn is the best...You are costing yourself money if you play purely on rb and dont hunt for the best overall games.