Simon
Got one of both, love the MGB Roadster for commuting/twisty bits and wind in the hair driving. But the CGT is quite a unique beast, disadvantages rare, heavyish steering (when fitted with the standard 17" steering wheel) but not as heavy as people would have you believe, and rediculously bad fuel economy in city driving (significantly better in the country/open road)
Advantages, more space than the B, much more power, quiet and refined, great open road cruiser, rarity and major pose value.
Contrary to poular beleif they will corner well at speed but generall a bit more forward planning is required than in the B
If I had to sell one I would finid it hard but if really pressed and it became my sole driver the C would probably have to go as it much less practical than the B for everyday use. Fortunately that isn't a situation that is likely to occur.
A good MGC will command a good price relative to a good MGB and unlike the Bs it doesn't amtter wether it is a GT or Roadster but you will probably have to wait longer to get that price (ie for the right buyer).
Much more important with the Cs to buy the right car, sills rusting is OK but floors or any front end damage isn't. With bitsas make sure all the important bits are there.
Parts that are getting hard to get: Difs (depending on ratio), good brake servos (can be reconned but needs a level of expertise that not many brake shops have), some engine bits (others are surprisingly easy to get) and brake and clutch master cylinders
Impossible to get: any inner front end panels,Speedos and Tachos and Steering column flex joint.
Auto boxes are pretty easy to get (unusually for the C it is common with several more common types)but manual and partucularly overdrive manual boxes aren't.
Wire wheels are easy to get (same as TR6) but the disc wheels and partucularly their hubcaps aren't, unlike the Bs and despite what the parts lists would have you believe there is no such thing as a 5 stud 15" Rostyle road wheel for the MGC
There has been a new run of heater taps so they seem relatively easy to get but they were next to impossible to get for a while.
Take your time and find a good (or at least complete) one
regards