Farming through the mods for PCs and getting those for PS3 would definitely be worth some cost to me. I'd love to have an array of modern firearms (M16, Colt 45, Desert Eagle, etc.). And I'd love to have something like the Aliens M-41A rifle too.
I'd also like to have more terminal entries and other data on what life was like in this world before the bomb and afterward. We have a lot of this in FO3 already (not so much in New Vegas) but more would be nice. It's so frustrating to have all these ghouls around and not be able to actually ask them what life was like back then. Maybe more museum exhibits with readable plaques or something.
So what would YOU pay for?