350 downloads still means its a popular download, seeing its on the first page of top downloads. But yeah, some textures are hard to imagine why they are so popular, when some of them took little effort to make and are the most downloaded, but they were the first textures made for popular ideas, and the general community doesn't always know quality when they see it.
Brawlvault shouldn't be limited, because I've seen plenty of quality hacks undiscovered with a low amount of downloads. The rules of the vault, unfortunately entirely unenforced, were designed to prevent the submission of recolors and low quality hacks, but that doesn't happen, and there are a lot of textures not worth downloading. Plus, I highly doubt KC:MM will do any clean up of brawlvault unless a texture is an issue of stealing or doesn't have the required stuff for an entry.
Anyways, you shouldn't worry about quality textures being unpopular at first, inevitably, they'll become recognized. Just make the textures you want to make, put in your best efforts, and disregard whatever the community thinks about it.