I didn't know there was a cheater. That sucks and how do you cheat on a contest like that?
I think it is entirely up to you. Making a vote mandatory is against the "rules" in the white papers but everyone does it anyways (bots weren't supposed to be on here either LOL).
Here is what I am thinking. You probably get a lot of people with dust votes to participate - that means no money for you.
And it will be a lot of extra work to double check that everyone who commented also voted and didn't just leave you a dust vote. Someone with a lot of voting power is not going to leave a 100% vote, so you can't stipulate that. At the same time, you don't want a bunch of 1% votes that don't count.
I think if you are having fun doing it and basically are willing to give up the money for the prize - go for it. Otherwise, I wouldn't.
From my experience, contests hardly ever are profitable for the person putting them on...