Well it depends.
I must say that I find most of it's known features pretty gimmicky. But if I happen to break my old DS Phat I'd have a hard time choosing between the light and the DSi. The missing GBA Slot bugs me just a little, but like I said the DSi features aren't thagt good, imo. So it would depend on the price, I guess. If it's not all that much more expensive than the Lite and the features prive to be used more than maybe twice in a game and the MP3 player doesn't completely fail in terms of audio quality, I'd buy the DSi.