I enjoy the Super Mario Bros movie in the same way that I enjoy the Flintstones movie -- it's a stupid, badly written movie that doesn't fit the mood of its source material, but it's got really nice set design. Flintstones had way better casting, though. And acting. And scientific accuracy.
In real life, I think there's a decent chance the X-Naut's X salute was a reference to the aliens' salute in Plan 9 From Outer Space. Or it could just be that they already decided on calling them X-something and that's a pretty natural way to make an X with your arms.