Hey! I remember these! S&S design, early 70's IOR MkI... a small classic. If I recall it might have been a 1/4 tonner. If the boat is in good shape, it could be a great choice. If I recall, these where built like tanks. I'm guessing it's a solid glass hull. Sure, it won't be super fast, but will go to windward well. Resale value? Not much, but look at it this way. If you pulled the engine out and sold it, sold the mast and keel for the going Al and Pb scrap rates, you might have your 2500 and a couple handfuls of change back.
Don't assume that because the boat is sailed regularly that it's in great shape. It might be, it might not be. An offer and survey? Maybe, but again, if the engine is in good shape, it alone is nearly worth the price.
The Northstar over the Catalina or visa versa? Which boat speaks to you? Which boat makes your heart sing? Contact the owners and go have a look.