I don't own TW3 yet, but yes, I also have now found a game my GPU (AMD HD 6950 1GB) wouldn't be able to run.
I won't buy a new GPU though. What I'm gonna do, is finish all games I have in my backlog and then buy all wishlisted games my GPU can run, and play those as well.
I know this is a long term plan and will take me 2 to 3 years.
But I think buying a new GPU while my current one can still play 95% of the games I want to play, is ridiculous.
edit:
TW3 can wait. If Rockstar can scale their open world game to 1 GB VRAM GPU's, Compact Disc PR REKT should as well, considering the latter should be more "PC friendly".