There aren't many around.
Howmanyleft shows around 500 (and falling about 10% per quarter). That's all Cinqs, not just sportings. If that continued at that rate, they'd be extinct from the road by around 2022.
In 2000 there were around 45,000.
Sportings are the more collectable but a clean, standard 899 will always be collectable too. Just wont reach quite the prices of a Sporting in the same condition IMO.
Condition wise, there's really now only 2 camps. "In need of saving" or "saved". They aren't cheap runarounds anymore, they are enthusiast cars. So you're either looking at one which has already been in that hands of one, kept, maintained and restored, or a totally neglected one. There's nothing in between. Truthfully, there's more bad than good out there now, hence why the good suddenly are being advertised at a huge premium.
The most common ailment is rust on the rear inner arches/boot floor seam which can spread up to the rear panel, mechanically head gasket failure is the most common one, clutch issues (thrust bearing mostly) tend to be the 2 reasons they get parked up.