I bought a 28k mile 360 in October so have some ideas for what to look for:
1. Clutch on 360/F430 is expensive, $5500 - $7500 depending on indy/Ferrari. Check clutch wear. If you have the early TCU (99-2002), then some get neutral jumps between gears around 70% wear and higher. This is what my car was doing, but I put a CS TCU (very hard to find, a 2003-2004 360 TCU is a good alternative and almost as good) and that fixed the neutral jumps and the car shifts and blips better than perfect now. Hope to get close to 100% out of the clutch now, but like I said, it would not have been possible with my earlier year TCU it seems. Regardless, price clutch wear into purchase price.
2. Belts - Are about $1800/$2500 at indy/Ferrari. Then $1k-$1.2k on your traditional annual maintenance. I had a full major, all fluids/belts changed, full inspectiong, for $2.8k.
3. Headers are better on 360 than F430, but look for any burn spots or cracks in PPI. Only 1999 cars did not have precats, the rest do and sometimes overheat and fail from the precats.
4. Check all the other obvious parts - brakes (pads and rotors), tire tread, ect.
Otherwise, that is about it. I agree that a good thing about 20-30k mile 360's is that they have appropriate miles (2-3k miles a year at least) and were actually driven enough to expose most potential problems by now. I've put on 1500 miles on my car, it's pure automotive bliss and I feel like I got the deal of a century
(not saying my price was abnormal, just that the 360 itself is a fantastic deal and I got a fair or better price ).
ETA: If your hypothecial that a full major (belts + fluids) for 30k service was done, as well as the clutch, then really you should be good to go other than brakes/tires.