To maintain MO alive and well, we need a regular flow of good questions, and not too many bad questions. It seems to me that one has given more weight to the latter, forgetting the former which in my opinion is more important. To the limited extent that the reputation system can do anything about the situation of question, we should have our incentives right. A good question is very important, perhaps even more than a good answer. But we're all afraid of bad questions getting voted up by too many times. Those questions often has a large number of positive vote, and an almost as large number of negative votes, hence in the current system give the OP a large total reputation. The -10 reputation should in a large part solve this problem.
To prevent abuse, we could increase slightly the cost of down voting to 2 or 3 reps, and raise the minimum amount of rep to be allowed to down vote, from 115 (which is the StackExchange bonus plus epsilon) to say 200 or 300.
Edit: After reading the comments and thinking a little bit more about it, I don't think any more that my proposition is a good idea. There is probably no miracle solution for inducing a lot of good questions with few bad ones.