My first qualm would be assuming that, for every tournament won, the spriters or artists creating their media aren't willing to do so. Artists are not dispensable and unless we're paying an artist to hang around Reborn, it's inherently unfair to ask the artist to create something unless they are absolutely willing and consensual.
The next issue is the frequency of these tournaments, as mde mentioned. The spur-of-the-moment tournaments oughtn't have rewards of such a great caliber as a sprite- back to the prior point. Without a proper format nor plan to these tournaments, users could be unfairly more likely to win a reward, without regard to actual tournament skill- if a tournament occurs when there are few users online, one is more likely to win, statistically.
I currently see our options as twofold:
-We maintain our current course of action and allow users the chance to speak upon joining the server for the first time. It is inclusive of any user not previously banned or muted, though it allows for spammers.
-We adopt a strict muting policy. Messages that do not contribute to server discussion are looked on as potential spam and may beget a warning or mute. It's a rough approach, but would cut down spamming. This approach would mean quicker mutes.