Funny you should ask. I used to own one quite some time ago. Obviously they were built in the early 70''s, most of them, so you should get a good survey.
I thought it was one of the best 30 foot boats made. 5'' draft, 9'' beam, very well built and sailed extremely well. I sailed mine to Bermuda from the Chesapeake and it handled very well. Strong boat, nicely laid out for off shore, assuming you don''t try to put too many people on it.
The longish keel and skeg on the rudder made for excellent tracking and a decent turn of speed. I also raced it some, and it had a good PHRF rating for its size.
The interior of mine was a darkish tone of white, so in retrospect I would have hit it with some pure white paint inside.
The original motor was junk, and has probably been upgraded since built, so check that out carefully. Motor access is great, but it is a bit loud when running, since it is in the center of the main cabin. I used a Navik wind vane and it handled the boat very well, even when sailing downwind in heavy seas--with only 28" of freeboard aft, it handled much like a submarine--not a lot of windage and tons of boyancy for the size.
I loved the boat and would recommend it highly.
By the way, I also (at a different time) chartered the Tartan 30 many times and spent lots of time on them. Similar design, by S&S, but the Tartan had a 10'' beam for a little more room down below. Sailing characteristics were similar, but I believe the Yankee handled sea conditions a bit better.
If you have more questions, let me know, "email@example.com".
BYW, Let me know which one you are looking at--it would be a hoot if it were my old boat. Not too many of them were made and ended up on the east coast. I sold mine on the Chesapeake in Annapolis.