How's your current machine treating ya? If all is well, I'd buy AC.
It is doing just fine.
The only issue that I have had over the past 8 months of ownership was a slightly "creaky" hinge. I took it in for repairs at an Apple Authorized Service Provider and they told me that they "realigned the screen/hinge". Honestly, I don't think they did anything to it. I was kinda being a tad O.C.D.
And the noise eventually went away... I could tell that they were kind of shocked that I was even asking them to fix this. The noise I was hearing was so faint that the technician had to turn off the Air Conditioning and the demo machines in the store just to hear the sound! (Call me crazy lol)
Other than that little incident (if you can even call it one), I have had no other problems to report. I have had Parallels crash on a me once or twice (it ended up crashing the entire machine). But I attribute that to Parallels compromising reliably for speed. I've never experienced my machine reach thermal shutdown. I have seen my temps hit 100 C, but never for an extended period of time (and that was doing a yes > /dev/null stress test). I usually idle between 36 and 45 degrees (which seems to be on the cool side for MBPs).
Just recently my machine started making that notorious metallic noise after I opened the lower case to do some routine spring cleaning (to clean out dust). However, I just took the lower case back off, realigned it, screwed the screws in a star-pattern and the noise magically went away. Problem solved...
I am highly considering taking the ($400 to 500) that I would have spent out of pocket to buy a new MBP (after selling my current 2010) and purchasing a decent 160GB SSD. I think for my uses, I would see a much bigger speed boost from a SSD than a processor bump.