I'm also new here, and in my very first search, I find this thread all nice and fresh. Perfect.
I, too, am considering the install of a Mac Mini (2006 Subaru Impreza WRX/STi). I'd already trolled the forum for info before registering today, so I was considering many of the things the OP is.
Mac Mini + Carnetix PSU + (for me) a 7" touch screen. I originally considered putting it all in the dash, but that might result in heat buildup. I'm 90% sure I'll be putting the Mini and power supply in the glovebox. Anyways, sorry to hijack there.
Quick questions related to topic:
1) Would it be better to have an older G4 processor (which run pretty hot) or one of the lower-end Intel-based chipsets in the Mini?
2) If you don't have it wired to a knob of some kind, is it a PITA to adjust the volume through the touch screen?
3) Are there any surprises we should look out for that we haven't asked about?
Subscribed. I'm a transplanted Southerner in Detroit, so this is how I spend my time.