He's done a bit. He produced an album by The Triffids in 1987 as well as doing some stuff with John Stewart.
I always assumed he'd not done much outside his own stuff/The Mac because he just likes to spend his time working alone in his studio. I'd like to see him produced more stuff (he can produce an album for me!) but not if it gets in the way of his solo stuff or more Mac.
Here is an interesting site with lots of credits for albums he's been involved with in one way or another:
http://albumcredits.com/Profile/3792...le/Albums/3792