I had an AWD 964 C4 and now I have a RWD 964 RS America. Both are great on the track. I felt the C4 was more planted but at the end less fun. A RWD Porsche is more difficult to drive but in my opinion more rewarding.
As far as the AWD system in the 964, I loved it. Liked it much better than the viscous coupling in 993 and later cars. Failures are rare, the system was engineered with no expenses spared. It was before the the bean counters stepped in. So yes it's expensive, yes it's overengineered, but it is highly unlikely you'll ever have to replace any of the AWD components.
BTW AWD was banned from road racing due to the "unfair advantage" of the Audi quattros in the early 80's. 'Nuff said
