I wouldn't. Very rarely can you have two mechanics that differ from each other like that. It forces too much development time.
That being said, I wouldn't mind fast travel if the world was actually worth exploring to make me not want to use it. In Oblivion, I hated fast travel because there was literally nothing in between dungeons. Almost 100% of the quests given to you in Oblivion were in the cities. I felt no need to actually explore, and it made me hate fast travel.
But Fallout 3 (and New Vegas definitely) had interesting worlds with lots of content spread around. This gave me incentive to explore and not use Fast Travel (at least in some cases), because I really felt like I would miss something. I never had that feeling in Oblivion.
Basically, the reason I disliked fast travel wasn't even fast travel's fault, it was a flaw of the world.