I'd say go for the 5d2. Pick one up new or lightly used and you'll love the quality. Sure, the AF system is pretty bad, but if you're shooting in decent lighting out on the street (or maybe even not so decent lighting) it'll still be pretty great. You have a nice set of lenses currently, and know what you want to get next. The 24mm will seem new to you, it's going to be a lot wider than you are used to, but it's great
If you're really concerned about cost, go for the 5Dc. I haven't owned one, but everything I've heard about it says it's still a great camera. What about renting one for a weekend when you plan on shooting a bunch of different stuff? It'll prolly cost you $100-200, but it'll really help you make up your mind. LensRentals.com has a 5d2 for ~$140 with shipping for 5 days rental.