I don't know where you're living, so I don't know what kind of sailing you're going to do, but I've been researching an upgrade to a 30 footer for a little bit now.
My top contenders were the Tartan 30, Catalina 30 and the Pearson 30.
There were/are several variations of the C-30 over the years.
Of the Catalina 30's, the 11hp diesel is woefully inadequate to push the boat into any kind of weather. The standard rig is short, and makes the boat a real dog in light air. The wing keel can be a real PITA if you run aground, burying itself into mud and resisting kedging attempts to get free.
The pro's are, the cabin is friggin' immense, and they ride like Cadillacs in heavier weather.
I'm out for a racer/cruiser that will do well in the light summer breezes of the Chesapeake, so the only C-30 that I would accept is the C-30 Tall Mast with fin keel. (and cross my fingers for one of the other stronger engines that they may have been equipped with)
Unfortunately for me, the C-30 is too fat to fit into my local slips at nearly 11' wide, plus they are on the "cruisey" side of racer/cruiser so I'm going with the Pearson 30.
Like I said, I'm not sure what your goal is, but maybe this information will help you.
S/V Old Shoes
1973 Pearson 30 #255