The CC 30 mk 1 is a great boat and not a bad beginners boat. It's a very forgiving heavy weather boat. I have a '77. It's a good singlehander- the great majority of my sailing is singlehanded- it's just a matter of rigging it to do so. I'd take issue with Jeff H that it's not a great racer. C&C's of that vintage have held our club racing fleet trophy for many years against a fleet of mostly newer boats (albeit, mostly cruisers). They sail very well to their PHRF rating. Granted, it's not a modern racing machine, but it's still capable of winning races. It's biggest downfall is very light air, and this is true with the other cc's of that vintage. The cc29 is a very different boat- a great boat, but inherently much less stable.
I'd be suspect of the boat with "a large blister". There are a lot of cc30's on the market. The most common known issues with them:
1. Keel to hull joint- "the c&c smile". Not a hard fix usually. Often just retorquing keel bolts will keep it from reoccurring
2. Wet decks-- water intrusion around fittings. This is a biggie.
3. Mast step failure-- wooden supports rot out. Not a hard fix.
You can get a boat in decent shape with average equipment for about $25k. Much more or less than that and I'd be suspicious.
Don't skip the survey.