I could be wrong, but isn't New Reno the only Fallout 1/2 location even remotely close to Vegas?
Depends on how the mapped area of New Vegas is placed. If New Vegas was in the middle of the map probably the closest place would be Necropolis or Hub. After that it would be Vault 15 or NCR and after them New Reno and abandoned Broken Hills. But it really depends much on the placing of the area. Also Necropolis is little bit questionable, is it really in Bakersfield or in the location of Fallout 1.
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Oh and getting bit off topic here. I wouldn't see any point going back there, it was destroyed 120 years ago, was excavated by Enclave and gave birth to a new generation of Super Mutants, haven't we seen enough that place. I would expect that it would have been sealed off again and would be a quarantine zone given the history of the place.
What comes to LA, if the place hasn't changed much I see no point in it either. It was described as a vast area of skyscraqer skeletons and dead bodies. Nothing interesting there, if the gangs over there haven't made a lot of changes.
In my opinion Hub would be the most interesting place, since atleast it was a thriving city full of merchants.