The scaler in the 3DS is horrible, you either see things small (original size) or with a horrible scaler that is both blurry and makes some pixels distort and seem double pixel (oh, my eyes hurt when reading text).
I use 3DS XL for DS games, but it doesn't look exactly good. I would understand the charm of a DSi XL where no pixel distortion is visible, you just see all even identically shaped sharp pixels, which is great.