I'm thinking about getting an OCR C2 or C3 but I don't know if the year matters any. Do the frame designs change from year to year?

I went to this bike shop today and asked the kid there, he said that the metal frames don't but the carbon ones do, they get lighter and stiffer as time goes on. Is this true?

Also, what's the maximum I should pay for a used 2006 OCR C2 in very good condition?