If I had your question, I'd ask it of the experts:
http://www.catalina-capri-25s.org/forum/forum.asp?FORUM_ID=3
They've had this discussion many times and can point you to their Q&As.
We had an 81 C25 for 12 years (-86-98). Bulletproof, rock solid. Other than a better gas tank locker, not much different than your 77. You could approach it a lotta ways:
1. What I got is mine and I have her fixed up just the way I want.
2. Whenever you get a new-to-you boat, there's ALWAYS something to be done.
3. When did you change your standing rigging? How about the other one?
4. Not all flips are = value.
5. How long do you intend to keep a C25?
6. If the newer one has better cushions and newer design cushions, hmmm...could be a real deal maker there!
7. Electrical system comparisons?
8. Engine reliability.
9. Are you aware of the headaches with a swing keel? We had a fixed, never had to replace a cable, worry about a mushroom or a winch under our stairs or the box in the cabin for the keel. Trailer headaches happen, too.
Build quality overall was very consistent and good.
The list is endless. And this from a guy who in 1998 bought a then-12 year old boat (1986) even after comparing it to new ones. By now, my boat's got twice the experience of what a new boat would have had! I replaced the standing rigging, got a newer furler than even the new boat would have had, like the interior better (even though they are very comparable but the teak on ours we think is better), we like the more compact cockpit, the wood and the dorades. My engine has 2400 hours, a new boat would have had as many as 1700, 'cuz that's what I put on the boat since we bought her; twice as many as the PO.
Your comps will be somewhat different, but those are the questions you have to ask yourself.
It ain't like cars.
Good luck.