I don't know what the difference between the 34 and 34+ are. I have a 1980 34 and really love it. With a nice clean bottom my boat will move in the smallest puff of wind. They are a well built boat that will hold its value pretty well and give you lots of pleasure.
If I remember correctly, the 34+ is actually 37 feet. (Don't ask me who came up with this idea.) I race against a 37+ (40 ft), which is a very nice boat. The 34 is a much older design, I believe. If I remember correctly, the 34+ was a good boat built during a difficult time for C&C. I would expect that it would be a very nice performance cruiser. If you are interested in racing it, you might want to go on SailingAnarchy, prepare yourself for abuse, and ask if it has a fair PHRF rating, as my perception is that some of the more recent C&C's can be a bit tough to sail to their ratings.