I know you don’t plan to, because who needs a shitty camera, but you are going to buy a DSi.
“Why?” you ask. “They play all the same games.” WELL, Nintendo has revealed that they can create games with special DSi-only features that obviously only work on a DSi. They also have the ability to make DSi-only carts, which would obviously be games that take advantage of the system’s extra RAM and processing power, or require the use of the camera or SD slot. Eventually, there will be exclusive software that can only be played on the DSi. (And this is on top of the already-exclusive DSiWare.)
This sound familiar? It’s basically the Game Boy Color business model updated for 2009. When the GBC first came out, all Game Boy games continued to work on the classic Game Boy hardware, but some of them were hybrid carts that contained color graphics as well as black and white. Eventually, the majority of software became Color-only, not hybrid, because the GBC had more power and could make prettier, bigger games.
So, yes, you are going to buy a DSi. It may not look like a “new system” right now, but one day, you’re going to wake up and find out that Fancy New Awesome Game is DSi-only, and, yep, you’ll have to buy one.