When should I get rakeback (if at all?)

In attempting to build up a bankroll, I'm currently going through bonus offers with signups. I haven't signed up for any rakeback accounts, simply because I don't know how worthwhile they'll be for me, since I don't play at a high volume and right now I'm only playing 2/4 and only 2 tables. I play maybe 3000-5000 hands a month, so I'm not really going to make a killing with rakeback.

So what's the point where it becomes more profitable to get rakeback on a site, rather than just bonus whore it up everywhere I can? I've been making 200-300/mo with just bonuses for the last couple of months and that seems like a lot larger than what I'd have made for the same amount of hands in rakeback money, but I'd like to be sure I'm not totally screwing up here.

So, is there a certain amount of play (hands/mo @ a certain stake level) that's going to get me a better deal than bonuses at various sites? (although considering there's no "real" party rakeback, I'm not entirely sure I like any of the sites that DO offer rakeback that I can still sign up for... so I'm not %100 convinced that rakeback is going to be more profitable than my normal profit at party's 2/4 game anyway.... so I need some convincing here)