For what most people are doing on Macbooks, I doubt you'll be able to notice any real world performance differences.
If you're a power user, then maybe. But then again, why would anyone that needs a significant amount of power in their notebook go for the Macbook when they can opt for the pro?
I wouldn't worry about updating to the new MacBooks until you start getting issues with normal tasks problems loading the OS properly.
Either that, or wait until it's just simply too ugly to look at from use hahah.
Only the people on Mac Rumors update their Macbooks/MPBs to the newest / greatest thing. Real people can't afford to do that every month. If I wasn't a college student, then maybe I'd be able to afford to do that xD.