There are many factors that will influence the market and the values of C3s. Some is supply and demand. Not only in C3s but in a host of other cars. For example: a person with a certain price range looking for an older car may not have the C3 on top of his list. He starts looking at the late 60's early 70's muscle cars and finds out that these are out of his price range. He looks at the C2 market and again he finds out his pockets aren't deep enough. He then moves down his list and sees he can afford a C3.
When looking at appreciation, I look at percentage move not dollar move. I would rather have a $10K item move 6% ($600) than a $20K item move 4% ($800). Any C3 in poor condition needing work due to neglect is not going to fetch anywhere near the price of a nice C3. There seems to be a higher percentage of chrome C3s that are now repaired due to the previous neglect. This has driven the average cost of this group upwards. The mid C3s range quite a bit. With almost 50,000 being built there are thousands and thousands of neglected cars out there driving the average cost down. These are affordable and still carry the name Corvette. People buy them, do as little as possible to them, drive them until they need more work, then sell them at a low price. It's only when a good owner buys it that the TLC is done to it. One of the problems is that the price of the car goes up, but the owner will sink more (cost of the car plus repairs) then he will get back. The biggest advantage the the early C3s have is the lower production. As for the style, that is debatable in my opinion. Back when I bought my 76, the 69's were selling for less. I choose the 76 because I liked the way it looked. My preference still hasn't changed.
As long as there is an interest in the 60s/70s cars the prices in generally will go up. Will there be an interest over the next 10 years? I think so. 30 years from now that may not be the case.

 

Well my '76 may be no collector's item for decades but I think it may take me that long to get tired of it enough to sell. Wife and I love the car and regarldess of whether it makes dollars and sense, I have boatloads of ca$h tied up in the car. It's insured for $20K and I would take a good sized hit if something DID happen to it.

But I can tell you one thing: it's built MY way by ME and I love driving it. Regardless of what it's worth.

 

, and thats the way it should be