I've had a DSi for months now, and I think despite the lack of GBA slot, the other features were well worth it in the long run. Take for example, Mighty Flip Champs
and the animation tool Flipnote Studio
. Granted, I don't pretty much use the camera, but then I find not much use for the GBA slot considering I have a GameBoy Micro. (Yeah, I know I wouldn't be able to use the Taito paddles for Space Invaders Extreme, but then again the score is not counted when using it.) The browser has recently released an update, so its performance is already upgraded from the already miles-better-than-the-original-DS-Opera browser for the DSi.
The sound quality is exceptionally good, too. I hated the somewhat scratchy sound the Lite has in its audio, even when using headphones. The DSi pehaps has the loudests speakers of any handheld out there, and listening to Chrono Trigger with headphones using it really makes you appreciate the bass.
And yeah, the matte finish is a big plus.