I've got V1s, V2s, V3s, and V5s. I'm slowly coming to accept that 3dfx hardware is mostly unnecessary. Modern computers with nglide can run most things. Heck, even Mechwarrior II, EF2000, and Archimedean Dynasty can be made to run nowadays. As time goes on, there are fewer and fewer games that won't run. If you have an FX5900 Ultra in your Win9x box, glide wrappers will run games better than real 3dfx hardware most of the time. Even a GF4 usually does a better job.
I still like to have my V1 cards for Mechwarrior II, EF2000, and Archimedean Dynasty because it requires a pretty powerful machine to get them working otherwise. Aside from that, the reasons for me keeping the other cards are out of pure nostalgia. I would sell my V2s and V5s before I ever sold my V3s. IMO, the V3 is just the most compatible and all-around good card to have for a pre-2000 legacy machine. They just work.
If I knew how expensive V5 5500 cards were going to get, I would never have done a cooling mod to mine. Even though I've improved the cooling, the mod cannot be reversed since I used thermal epoxy. I'm sure this makes it far less valuable, even if it makes it more reliable.