The militant GM fans took over the thread on corvetteforums, check it out, realy awesome entertainment.
The demand for the Corvette incresed indeed, by no means x3 as you stated but it incresaed the same amount as the C6 is better than it's predecessor. The reason is simple, Corvettes are selling so bad every dealer who made the mistake to order one is selling them way under original price. The discounts on those things are magnetic. Now owning a car nobody takes serious, but with proper performance numbers and the new ability to drive a curve, is, compared to reputable sport cars like Ferrari and Porsche you mentioned, realy cheap. The Z06 is, without question, the best 'bang for the buck' but sportscars got a slightly different definition over here. Good performance numbers 0-60 or 0-100 aren't sufficient to sell cars. Sportscars are sold beeing successful at racing. New technology invented for racing are requested and required to make a sportscar successful and the Corvette doesn't have them. Of course you don't necessarily need newest technology to go fast around a corner but it's nice to have them and that's why decades old technology fitted into a good car isn't good enough to make it a success on the market over here. Your claim other sportscar brand customers jump off to Corvette isn't true. There've been 24 new registered C6s in germany last year, 5 new so far this year. Can't tell numbers for other countries but even the NSX has beaten those numbers in it's last production year.
Regards
Klayton