I've never once bought a game console just for one game or one series. I HAVE however bought a game console on a whim because it looked like it would have good games and then bought only one or two for it (Virtual Boy and NGPC spring to mind). I also first bought my Playstation for an odd reason... I had a friend with a Playstation. When Mega Man 8 came out, it was only available for Playstation and Saturn. I weighed the options of which version I was more interested in, and decided to get the PS1 version since I didn't know anyone with a Saturn. After a while it became apparent that the PS1 had a slew of games I wanted, so I bought one anyway.

I will never get a game console JUST for a Final Fantasy game. I WILL get a console if it has a Final Fantasy game and at least 5 other games that I want. For this reason, I WILL buy a DS (Kirby Canvas Curse, Wario Ware, Feel The Magic XX/XY, Puyo Pop Fever, Polarium, as well as the upcoming FFIII and FFCC), but I'll wait a good while longer before picking up a PSP (Other than Lumines, there's nothing for it I particularly want, so the promise of Crisis Core isn't enough to pique my interest, not yet anyway). Same thing happened when I got a Gamecube. I asked myself "do I really want this?" then looked at what was out for it. I decided there were enough games for it that I wanted to warrant buying one (Zelda: Wind Waker, Super Smash Bros. Melee, Viewtiful Joe, Soul Calibur 2, Resident Evil, and finally FFCC).

I reccomend the same to everyone. Granted, the best policy would be to just buy every console so you won't have to limit your options, not everyone can afford this. Just buy the consoles that have a good amount of games that you already want. Even then, try to get it used.