Personally, i've always found advantages to buying computers in time with releases of new major CPU architectures e.g. Core 2 Duo, Sandy Bridge etc.
The resell value of the computer stays higher for longer, your new kit is more likely to support the latest OS's a little longer. The outer cases of the machines may change with a refresh, but overall the revisions to components isnt as big. less of a kick in the nuts when watching the latest product laugh keynote 😎
I have a late 09 iMac rocking a core 2 duo which looking back was a mistake as i should have waited 2 months for the Nethelem chips, the performance increase was large. Because of that my iMac lost half its value in less than a year, where as the first Core 2 duo iMac (late 2006) kept half its value at 3 years with a cheap ram upgrade.
I'm holding out for Haswell as my machine is okay for me for now and still in warrenty. Unlike me though, it sounds like you dont have a computer right now, so would be silly not to just go out and buy something you need. You could get your Mini and see how you feel with it in a year? You may still be happy with it then, or if you feel you need the extra power you could sell it and get a new one