Re: stingray 1989
For a nearly 20 year old boat I wouldn't worry too much about the quality of the brand nearly as much as the current condition of THIS boat. IF it withstood 20 years use and is in good condition, that's about all you need to know. now, the type of ride it has may be important and different hull styles have different ride characteristics. As was said, a newer Stingray is lighter than most similar boats and most say it's faster (per similar HP due to weight of course) and rides a bit rougher in chop.
Remember, the engine is what you're paying for mostly in a boat that age. So check it out closely and run it. Tell us what is is also so folks can comment on power and such. For water sports, the engine is what matters most! The size needed depends on how many and how heavy your typical "crew" will be. throw three or 4 adults and a few kids into a little boat and it can significantly increase the power needed for water sports.
Someone mentioned the chance of wood rot - again an 18 yr old boat has this concern. If the vinyl is not ripped and the boat looks in very good shape, at least your odds are much better that it was very well cared for and maybe didn't get wet under the deck and rot the stringers or transom. AT LEAST take a rubber mallot and tap around the transom to find any obvious rot issues there.
Lastly, you should be able to get that age and size for maybe $3k or so. IF it's in great condition, which is somewhat hard to find going back 18 years, then maybe closer to $4k to keep your search for a nice boat reasonable. It could take a long time to find one priced just right AND in great shape, so a few extra bucks may be worth it!