What's the asking price? You can get a decent idea of Commemorative Edition prices by looking at Saabnet's c900 classifieds page -- scroll through them all. Some of these cars are going for pretty decent money (well, relative to other Saab 900s). The most expensive c900s in the used market appear to be the so-called "bumblebee" yellow convertibles w/SPG plastic (they are not, technically, SPGs).
It's probably worth a nice email to the guy who runs the CE website, who IIRC is pretty active on forums and owns a few CEs.
Regarding the rebuilt title: I would want to see damage photos. Also, as you probably know, the front fenders are welded on, so any front end work will need to have been done well to avoid rusting. If the repairs are decent, and you want the car, I'd say buy it. Frankly, a fresh transmission (WITH RECEIPT and rebuilt by a Saab indy) is a big plus.
CEs had a few interior parts unique to them, so be aware that replacing them could be $$, in case you'd be wanting to keep the car pristine and correct. (The distributors are rare, too.)
Regarding c900 rust, if you're not in a saltfree part of the world: look under the rubber at the bottom of the doors, the spare tire area in the trunk, the axle tunnels in the wheel wells, and the fender seams underhood. If you are serious about buying, insist that you be able to look under the carpets in the front footwells, which can rust well after water leaks are fixed because of the open-celled foam used for sound deadening.
I don't think the c900 will ever garner the enthusiast attention that the E30 does. There aren't many weirdos out there that love the car. 
