Overall, it's not difficult to recommend the 3DS XL to any number of people. If your hands aren't tiny, you're going to have a better time with its extra gripping room and screen space. If you find the 3DS's screens disagreeable for any reason, whether that be size, 3D wonkiness or glare, the 3DS XL might hold the solution for you. And if you really don't care about the lack of a second control stick without a costly, cumbersome add-on, then there should be nothing holding you back from picking up the new 3DS XL.
Even owners of the existing 3DS could do worse than a trade-in, and it's easy as pie to transfer your profile, save data and games from an old system to a new one.
The 3DS XL beats the 3DS in almost every way. Now that I think about it, maybe that David-Goliath metaphor doesn't work so well after all.