I see this going three ways.
If the Gen V is a major home run, wins car of the year, beats all the competition, gets props from the world press and is the most desirable new model out there, then I think it will help drive the price up on all Vipers....or at least keep them from dropping off the face of the earth. Everyone wants to be associated with a winner, even if it's not a Gen V, it's still a Viper which might just be the hottest name in high performance for the next 12 months.
If the Gen V is a total bomb and is a failure, the Gen 4's might actually benefit from this and keep or at least not fall in value as fast. The purists will look at getting the last of the raw 600 hp beasts and saving a ton of dough over buying a new Gen V.
If the Gen V is just so, so,....nothing to write home about but not a bad car, just not an iconic beast, then I think Gen 4's will continue to lose value at the current rate.
I'm hoping the Gen V is a GRAND SLAM home run, regardless of what it does to my cars value.
Cheers,
George