There's no money to be made flipping it, especially if you're thinking about trying to do so on eBay/amazon.
I would just keep it.
Well, my flipping plans are more "take it by my local game shop that deals in retro and new stuff and see how much they'll give me in credit"
I do have both a 3DS and a DS Lite, so this DSiXL is redundancy on top of redundancy.
I'll admit, though, I've got a few unnecessary game systems around, especially in the handheld category.... I've got
multiple original "gray brick" Gameboys, which are all kind of pointless since I have a Gameboy Color... which is kind of pointless since I own a Gamboy Advance... Both the original and SP. I also have a GB Micro which, of course, can't run the pre-Advance games, but is kind of unnecessary in and of itself.
I could honestly part with all of those except the SP and the 3DS without any real problems. (...Except I'd have to use a Gameshark to reorient Kirby's Tilt 'n Tumble

). But I keep those other handhelds around because of nostalgia and sentimentality... and because they aren't worth much, unlike this DSiXL.
I've also got two Gamegears (one non-functional and one semi-functional)... and I bought a PS1 loooong after I had a PS2 because it was $3 at a garage sale.
... Back to the topic at hand. I wasn't impressed with the DSiXL initially (this is the first one I've spent any real time with), as its menus just made the display look poorly pixelated... But after playing Thor (a sprite-based beat 'em up by Wayforward) on it a while, I am having some second thought about trading it in.
It'll all come to how much they offer me for it.