I've found two problems with old boats:
1) If left in the sun, the fiberglass laminate becomes brittle wth time. Ultimately this results in the bow breaking off in front of the front pylon.
2) Old boats just don't work as well. Hobie Cat made a number of updates over the years:
- The best used boats are from 1996 or newer. These have integrated traveler tracks and lots of ease-of-use items like Harken cam cleats and a low profile 6:1 main block sheet assy.
- The mid-80s boats got a recut jib allowing really good mast rake.
- In 1982, Hobie changed the mast step cup and shortened the shrouds to allow more mast rake.
From what I've seen, you must spend about $1500 just to get a good serviceable boat and trailer (at least in Colorado). If you buy a cheaper boat, you'll spend as much or more fixing it up.