YES! Thank you for the suggestion, Wiggy! I was afraid I wasn't going to be able to use the "world" normally found on the Japanese cover, or that I'd have to shove it into a corner on the back, since I couldn't find it at a good enough resolution... but as a monochrome background object, the lack of clarity on it works perfectly.

I've also typed up the back text (at least the original version, may or may not make some tweaks to it), corrected the barcode, added an outline to the "SUPER MARIO BROS. 4" text, and adjusted the logo colors to match the US box better.
I'm definitely going with the blue background, so I changed the 4 from the original dark blue (which worked well on the yellow Japanese box) to yellow (which actually matches the 2 in the GBA port's title) ... I'm not sure if that's how I'll keep it, though...