i feel like with a bunch of tweaks, the style riders contests COULD work. maybe putting in some rules to prevent players from turning in full sets or mostly full sets (eg on the submission screen, you cant submit if you have 2+ items from a set on your horse or on your player, counted separately)
also something to help with voting. it takes too long, so maybe you can filter through submissions somehow? (eg looking rhough the lowest votes, highest votes, randomized, etc) and also the "skip" button should be separate, with a "reject" button being present if you actually want to skip an outfit and return to it later
BETTER THEMES WOULD HELP TOO. what are we even supposed to do for "fish are friends not food." maybe also having a vote for themes could be fun!! the themes should be doable with VARIOUS items already in-game (not just a single set, not just a single item, but MULTIPLE items) and should be related to... y'know... a horse game... oh and magic horses should be allowed.
rewards should definitely be better, too. everyone that participates should get a shirt (i dont know if only finalists get the shirt or ribbon ive been a finalist both times lol its too easy to get in there), and finalists should get WAY more shillings.