People can keep saying this... but I don't believe it for a minute. Too many talented people here (Dennis, Vektor, Deg3g) have created quality, highly detailed versions of the original that would've looked damn spectacular on the big screen.
With all respect to the artists you mentioned, all they did was take the original design and added a few tiny extra things - it was still the same old boring shape - a dinner plate and some sticks. Seriously, the original Enterprise is one of the more ridiculous sci fi ships around (very much along the same lines as the Jupiter II from Lost in Space - can you see that being taken seriously in a film?) The engineering problems with the design alone are staggering (the center of gravity is actually *outside* the ship) the ST:TMP design for the Enterprise however was magnificent and one could entirely forgive the engineering problems because they turned the frankly ugly TOS ship into something exceptionally elegant and beautiful, not to mention, believable in scale and detailing. The TMP ship (or the Abrams ship) is definitely what Jeffries would have designed if he'd had a budget.
They simply could not EVER have put the original ship on the screen in 1979 or 2009 (even with extra detail) and expected not to be laughed at by everyone except a few Trek fans with their rose tinted glasses on. Specially not 2 years after the release of Star Wars in the case of ST:TMP. And we've had 35 years of further advancement of effects and design on top of that. You people just don't take context into consideration!