I agree with Joe and Andrew. While the performance numbers of the 2003 are predicted to be better than the current model's, the styling -- in the opinion of many -- is just not as distinctive. You're driving around today in a vehicle whose styling dates back 10 years, and still people see you and say "Wow! A Viper!" I don't think the 2003 will generate that kind of reaction ten years later. (Maybe "Oh, look! There's an old S2000!")
A thread on this board quietly came and died concerning the fact that, at this time, there are no definite plans at DC for a next generation coupe or a racing program. A pessimistic Viper fanatic could certainly not be faulted for interpreting that as an indicator of impending doom. Considering the current trend in higher gas prices, Congress considering higher CAFE standards for all vehicles (not just cars), and increased emissions standards, not to mention the downturn in sales and profits at DC and the German non-Car Guy management team, speculation that there will ever be a Gen III coupe could be seen as overly optimistic. If there is ever a mindset shift in the public perception that gas hungry vehicles -- be they SUV's, trucks or big-engined sports cars -- are not fashionable and not politically correct, the death of the Viper and its bretheren will come quickly.
Climbing down off my soapbox, what I was trying to say is that the current GTS may be the only coupe in Viper production history, so I wouldn't wait. Get a piece of history now. Also, there's a good possibility that you might not be one of the lucky ones to have the chance to buy a 2003 (or that you're unwilling to pay a premium to get that chance). So we're talking about the 2004 model year, which is over two years away. Do you really want to wait that long to "upgrade" your Viper ride? And if it's a coupe you really want, the earliest we could see one would probably be model year 2005 or 2006.
There's a lot we don't know yet about the next generation Viper. Yeah, 500/500/500. But how much better will that car actually perform than the current Viper, much less the slightly modified Vipers driving around with 500 RWHP? It's not like the Gen III is 500-600 pounds lighter. The Viper gained its reputation and image from clearly outperforming all its competition. But the competition is getting stronger. In 2004 will the Viper still overwhelm the others performance-wise? Based on recent rumors hinted at on this board and elsewhere, the Viper is going to need well over 550 HP to outperform the competition as clearly as it does now. While Team Viper may be committed to making sure that the Viper remains a solid "King of the Hill," I'm not convinced that DC management shares that conviction.
So I would not wait. (In fact, I didn't wait -- for these and other reasons, I sold my 97 GTS and bought a 2001 GTS.) If the current GTS's resale value dips or goes into the crapper when the 2003 becomes available, the value of your Gen I RT/10 will probably be similarly affected. If you want to match the performance of the stock 2003, the aftermarket can do it for you. You won't have the latest and greatest Viper, but you'll still have a car that, from the masses, generates that "Wow! A Viper!" response we all have grown to love.