So here's the thing about people joining for just the medal and why it's not that big of a deal.
There are always going to be people who put a half-assed attempt in to earn any participation reward like this. But, of those people, there is going to be a certain percentage who stick around the site because of it. They only joined for the medal, but saw what a cool community we are and how fun an event like this can be, and decided that maybe they'll get involved. Maybe next time they'll whole-ass it and maybe they'll become super active in the community, creating content, participating in other events, helping us test.
This effectively works as advertising for the site. A lot more people heard about the site and the event because of the reward, and that's a great thing.