I used to think that it wasn't worth it. And depending on how much it'll hurt your budget, it may still not be. But I spent a year pining after Fable 2 and it is NOT going to be released on PC. If you really want to play it that much, go for it. And when you're done with the game, you'll have a shiny new XBox360 left over, to play as many games as you want.
If you liked Fable 1 as much as I did, you'll probably like Fable 2 as well (despite its console-based issues, such as no hot-keys for spells/items/actions).
If it's one game that gets you off the fence to buy a console, then so be it. For me it was "Legend of Zelda: Link to the Past" and "Super Metroid" for SNES, and "Final Fantasy VII" for Playstation. I simply couldn't NOT play those games. Had to do it. Was the same with Fable 2 on XBox, and now I'm glad I did because I got my fix and now have all the other games to play.
The alternative is that you could spend a lot of time (and money) chasing after games that are NOT the one you really want. Maybe you can find some gems, but it's hit or miss. A lot of games require a significant time investment - do you really want to invest all that time in a game that isn't the one you really want?
Given that so many producers are moving to console-only games, it's not the worst thing in the world to get a next-gen console, so pick whichever one has the games you want and get on with it!