Their expressions make me smile, lol. It's cute! I think your vector is fairly good, especially for your first vectored wallpaper. Sakura's bangs are extra jagged though. I think it's good to shrink a large vector to get rid of those jags. Also, the outlines of the background items, specifically the school, is too thick. And because Syaoran and Sakura's outlines are thin, the depth is confusing (things farther away should be less clear/lighter outlined than the main focus in front). Oh, I like the simpleness of the background 8).

Generally, cute/happy wallpapers should be colorful in my opinion, and the colors here are rather dull (I see dark/dull colors as meaning sadness or depression). Then again, the anime art is rather dull too... anyways, good job overall!