The oldest suitable is the 2009. That one has a 9400M GPU which delivers GPU video decoding in XBMC. The prior model manages to struggle through 1080p content too by having the CPU take care of it, but it means the fans kick in badly.
I would say the 2010 is best, as it has the built in PSU and allows a BR drive to be mount.
I don't need BT, I programmed my Onkyo receiver remote to act as Apple Remote and it works with XBMC.
Old Mini's don't have USB3, but for playback it is no problem. Only to move large amount of movies over USB2 is not so fun. I try to do every movie transport over gigabit, so I don't mind. Gigabit is perfect for keeping up with the full speed of large hard drives.
Oh, for media center purposes, skip SSD. You're better off with a much cheaper fast HD like a Scorpio Black. That delivers 750GB for 60 bucks or so, and still doubles the speed of the stock drives.