I owned a 1976 Dolphin. It was my first boat in 1990 and gave me a real good boating education. Generally its a solid hull that will take most inside sea conditions. A couple of sore points I can remember:
1st - and this is a big one - the boat doesnt have scuppers. All water drained into the bilge so the bilge pump worked overtime. My boat actually sank 3 times at the dock because of too much water getting in and the pump not keeping up. No matter how much back up I gave her, without drainage its an uphill battle. You cant be with the boat every day, and shit seems to happen most when you're away.
2nd - I was the 5th owner, so the hull had all kinds of do-it-yourselfer modifications. patched up drill holes in the transom, hundreds of old wires strung all over, etc. Took me a while to straighten most out, but damage was done that I wasnt prepared to tackle on such an old hull. You say yours was maintained well, but beware of things not apparent. FYI - pull out the console and see how the gauges are wired.
3rd - its not a dry ride. Even with a brand new 200 hp suzuki on the transom (mounted after transom repair) the bow dug in.
4th - the split windshield design is not great. Gives access to the bow but its a pain to get up there, and when there its not the safest feeling.
5th - wiring for everything traveled below gunnels / freeboard. Steering and engine harness, all wiring for gauges and electronics, everything was strung from stern to bow under the gunnels and tie wrapped in a bundle. Difficult to work with a bundle like that (hence the large # of snipped wires left in the bundle for me to figure out. Plus - I was always getting hung up in the bundle by my rods, boat pole, etc.
6th - see recent post by Awnuld titled "Fuel Tank Discovery". Its the same boat you're looking at.
7th - be wary of how its age has effected the internal wood and glass. Stringers, panels, bulkheads cannot survive unscathed after all those years. Even with immaculate upkeep and dry/inside storage, everything decays. Be careful and have someone with extensive knowledge kick the tires. I know a guy who bought a well maintained older Bertram only to have a friend fall through a soft spot of the floor during a fishing trip. He was convinced by the owners pride and apparent good looks of the boat that everything was okay, no need for inspection. Ouch. IMHO, dont buy it unless you get someone to run a moisture meter over the transom.
Positives - positive buoyancy. I said mine sank 3 times, but not a true sink. It took on enough water to fill the hull but never got to the bottom because of the factory blown foam under ther gunnels (and other places).
Decent storage for a boat that size - cabin is good size, lots of storage under split bench passenger seating, even a glove box. Mine had the oil tank inside the box which my captain's chair was mounted to. I pulled out the tank and used the box for anchor storage. The two transom seats were designed as coolers with drainage, but I took the batteries off the floor and used both for a dual battery set up.
Over all decent ride, felt safe. Pefect to learn your local waters in.
After I bought mine I did a lot of cosmetic work and mounted the new engine (a Suzuki that had a gravity fed oil system, allowing me to get rid of the oil tank as mentioned before). All of the seat cushions were redone with new foam, canavas, marine plywood, stainless hardware. I installed 2 new batteries with a 1-2 switch and re-wired all existing electronics. Mounted two new bilge pumps. Installed a vhf and fishfinder with transom mount transducer. Plugged 100 holes all over the place. Replaced the rub rail and multidude of screws under it - what a mess it was under the old rail. Replaced the fuel sender. My first winter with the boat I pulled the hatch over the tank and let the whole area dry out. The way this boat is built -without scuppers - the tank is always in some kind of water. There's a pipe running from below the cabin down the length of the boat into the bilge area to carry water from the bow (now they use a bilge pump drain that pumps to a front scupper), which in theory is good, but without drainage excess water will surround the tank. After blocking the boat for the winter and pulling the plug you'll see what I mean - lots of water will pour out. But my tank - aluminum - never leaked.
Before I installed dolefins to the engine the boat would be slow to reach plane and tended to porpoise a lot. After the install I was pretty happy with the change in both.
I hope this helps. Good luck!
Looks like this is turning into a restoration almost for me, if I knew what I know now (cost wise) I think I would have gone younger/newer.