Well, finally I decided to dump all the stages backgrounds as I did with Hyrule Castle some weeks ago.
For all those people interested in remaking them, the link below includes the textures I dumped for now.
Remember,
this is a texture dump, not hires textures.
Download SSB backgrounds texture dump (1315kb)
Some quick notes about them:
1) A Background in SSB isn't a simple texture. It's made of vertically-tiled textures (37 for Training Mode, 44 for Characters Stages).
2) 4X textures won't work properly in DirectX due to a 1024 pixel width limitation in the plugin. So I recommend using either OpenGL or 2X/3X textures to test your backgrounds.
3) Some backgrounds (like Mushroom Kingdom) use the same texture several times, so trying to replace them with a totally different one is not a good idea.
4) The dumps include only the characters stages and training mode backgrounds (Bonuses, Metal Mario, etc. not included).
5) I've already made training mode backgrounds. They will be available in the next pack.
6) Training Mode Backgrounds are not the same size than Character Stages Backgrounds.
7) I added leading numbers to the textures filenames, so you don't need to worry about which texture goes where. But don't forget to remove them before testing your backgrounds.
Also, considering that the stages pictures at the stage selection screen are just resized versions of the backgrounds themselves, I remade them, and corrected the Hyrule thumbnail I did before to add the lines it was missing.
The attachment includes all of them.
These are hires textures. Put them anywhere in the SSB hires texture folder.