This is just a competition and try to be creative and submit whatever you have in mind and no need to be high profile artist to participate in these contest.
Yeah and foremost we shouldn't only looking to win the contest, well many people will join because they want to win, but we should look in the different way what's does we get while participating the contest. Of course our skills will improve since we're force to create the best art that we can make. IMO prize is just a bonus and motivational to win the next contest because Roobet have conduct multiple art contests every few months.