A guy at work is big into Craigslist and offered to sell me an i5-2400 for $20. I wanted it mostly because I have MacOS running well on this board, and $20 seemed like a reasonable deal to keep the install and get 2 extra cores (I have an i3-2100 right now)

What do you all think? Also, if you have a better 2nd or 3rd gen i5 or i7 you aren't using, let me know. With all the moving stuff, I'm not exactly rolling in dough, but I wouldn't mind a cheap upgrade for the old hackintosh.

I would take that deal.
According to PassMark this will give you about a 40% bump in power. That is a healthy increase.
I say go for it.