I've actually been resisting the urge to fire up Fallout-3 recently. Thing is, I've got so many mods installed, I can almost guarantee the game will crash on start up until I remember everything that needs to be tweaked. I MIGHT end up doing a fresh install and then re-installing mods again, one by one. That's a time consuming process on its own (but can, perversely, be more fun than the game).
Considering Fallout-4 LOOKS very similar to Fallout-3, I can hope that playing FE3 will help assuage my burning desire for FE4. I've finished FE3 probably three times or more, now, and frankly don't care much for the actual main plot any more. But just roaming about, exploring... that's fun, still. Particularly with mods that add new player housing, or even quest lines.... one mod adds a sister that acts as a Companion and has voiced dialog / responses to existing quest lines. Things like that can really bring an old game back to life.
Aside from the burden of essentially re-building the game the way I'd want to play it (fresh install, mods installed), I'm playing some other games (single player and MMOs) and I know if I start in on Fallout 3 again, it will CONSUME me and I won't get back into these other games. I've already bracketed out four vacation days in early November to play FE4 when it comes out, though, and I'll be ignoring ALL my other games at that point.