I look at this rationally.

A DS will bring you more happiness overall than a PSP will.

I havn't bought any system for one single game alone. When I got my DS, all I had in mind at the time were:

1. The ability to play FF1-6 advance on the DS.
2. "World of Mana" series. (Gonna play them atleast once)
3. FFIV-DS
4. Cooking Mama

And now, Mario Party DS and an aray of other games. The DS is prolly my most favorite item next to my iPod.

Either way, yeah just look at it rationally on what the PSP versus the DS has to offer you, and at prices too.