Apart from that, I agree - it's Q&A, not /r/funny, not a discussion forum. Though I haven't seen that many questions that aim to ignite such discussions.
Hiding stuff that doesn't below under the rug doesn't make the problem go away, fixing the problem does.
In a gamification environment moreover you need to make sure that the rewards are given for activities you want users to do more of. Participation in 'fun' questions is not one such thing. Since they get ALL the votes etc. they naturally attract more of the same 'fun' questions.
No, those 'fun' questions just have to go.
1. "Fun" SO / SE questions. 2. Serious SO /SE questions.
Given this, of course you want to encourage people to choose Option 2 as much as possible.
But there's also...
3. Do something else completely unrelated to SO / SE.
Time is variable with participation. By driving me off through closing and deleting things that don't fit your personal vision, you have reduced the amount of total work time available. Not just for the fun things, but for all things.
Gamification points are also not finite. But if you are really concerned with over-rewarding things that are too gosh-darned fun, just stop rewarding them. It's an easy fix. E.g., instead of marking a question closed, you mark it as just-for-fun; points stop accruing.
I guess what you could be saying is that time is finite for some particular group of people. In which case, you've introduced an us-vs-them dynamic, and are basically declaring that the system is about serving the desires of the in group, rather than all participants or all readers. In which case: have fun with your bat and ball.