There is a clear case of spamming in the kitchen design contest, and there have been tag-along entries that have nothing to do with the themes of the contests trying to capitalize on the higher viewership generated by contests to get downloads.
For the spamming problem, settng a limit, such as a max of 5 entires can solve it.
For the tag-along problem, MakerWorld will need to enforce this rule: " 6. Submitting entries that do not meet the contest theme will result in disqualification, and repeated offenses may disqualify you from future contests." . Perhaps MW can have an employee browse the entries once a day, and hide entries that are considered out of theme and give the uploader 48 hours to appeal. Or have a report function under each entry for users to report potential tag-alongs.
Added: Perhaps MW can modify the above rule to add some text to the effect of “uploading out-of-theme entries will disqualify creator’s valid entries from consideration of any awards”. IIRC, there have been at least one case where a designer uploaded some valid models and then also uploaded some out-of-theme models.