Saw a 2004 go for $58k yesterday. I didn't catch any details about it though as it was just on a TV out somewhere so I couldn't hear anything. Granted I also don't really follow the market regularly and my only point of reference is when I bought my car something like 8 years ago, so 58 actually kind of surprised me. Back when I was shopping that was closer to 2006 coupe money or even some gen 4s.
I think the 3rd and 4th gen still have a ways to climb on prices in the long run as I don't feel like they have quite hit their niche yet. The gen 5 really spiked when they stopped making them and the earlier gens have really spiked as the kids that had them as bedroom posters grew up and could buy them so I feel like they are more fueled by nostalgia than anything right now (also because they stopped making them). I don't think the gen 3 and 4 have ever really had that nostalgia factor for anyone. They aren't "the original" (gen 1), "the LeMans racer" (gen 2), or "the last" (gen 5). The gen 4 has the ACR going for it, which has always been valuable, but the gen 3 has basically nothing but rarity (compared to other cars, not necessarily Vipers) in its favor as far as collector prices. I think prices might sag or stagnate in the near future when nostalgia wears off and the next generation of buyers starts buying as I don't think they have the same kind of attachment to the car. Feels like the current generation is more likely to buy stuff like Hellcats, Demons, GT350Rs, etc. But in the long run I think they'll go back up as rarity takes over, EVs become more common, and eventually as the first generation of buyer starts retiring and having money to spend on the cars they used to have as kids (like the muscle car boom). You figure they only built something like 30,000 Vipers in the whole history of their production, so that's got to carry some weight. For the most part they rarely even built more than 1000 per year, so any one Viper is still pretty dang unique.