I know that I don't need to upgrade from my Lite, but if I were going to get a DSi at this point, I think that I would choose the XL over the normal version, if only for a bigger canvas when I inevitably used Flipnote Studio. I think that with all of the text and creativity-heavy games on the console, it's not a bad idea at all to allow gamers to pay for bigger text and more room to draw/write with, but it's also not the most necessary upgrade Nintendo's ever come up with, especially not with the 3D model looming on the horizon.
(Also, I saw a Powerpuff Girls emoticon on the sidebar and wanted to use it, so here is an extraneous smiley. :buttercup )