I agree with much said here, however; if I am not too late I would like to offer you my 2 cents:
Riley is right, a 1969 to 1973 Vettes are the most desirable C3 Vettes because of their chrome bumpers. Vettes from 1974 to 1982 are not as much because the HP went down due to government regulations. HOWEVER; a good 1976 is a collectible in its own right, if the vehicle is mint and all original it will be very valuable, maybe not fetching crazy prices right now, but imagine 20 years down the road. Right now the price difference is due to the HP originally from the factory, but funny enough, the most expensive C3 is a 1970 ZR1 with a small block, so it is not the power that makes them valuable, but originality, and how rare the car is or will become. A perfectly original 76 will be pretty valuable in the future, as it only becomes more rare.
That being said, a 1976 Vette that is in mint shape and very original is worth $20K.... a so so Vette not numbers matching, bad paint, etc it is not worth more than $8K. Paint alone would be around $7K for a quality job so you are better off spending a bit more for a perfectly sound all around Vette. History shows that every year is special on its own merit... would you say yuck to a 1964 Stingray? no way! but 20 years ago you might have because you'd prefered the 1963 split window...and dont buy a SO-SO Vette unless you are looking for a big project!!!