I wouldn't bother buying now. The current machines have been on the shelf for what, ~8 months now? I doubt Apple will update before the holiday if they didn't now, they probably won't bother updating until February-April next year (and I'd bet it won't be until the latter end of that timeframe).
Honestly I get fairly tired of Apple stretching out their upgrades to 1+ years at a time; it was bad enough when you had to wait 8 months between real refreshes, now with them being even less frequent I am loathe to give them a dime unless something is extremely fresh. I don't like the idea of buying the same machine at the same price that has been out for 8, 12, or 14 months; it's basically close to a year old already.
I'd just wait until 2015 at this point, you're halfway there and your current computer works fine.