I think that in general bad questions are dealt with fine, the majority of them are closed very quickly (as in 5 - 10 minutes) from what I have seen. If there is a question that needs to be closed faster you should be using the
flag button to draw a moderators attention to it.
The other issue is it makes the user interface more complex, which should be avoided. Rather than having the simple Need 3 more votes to close, it could end up need 3.75 more votes to close which makes no sense whatsoever.
The last issue is that, sure I have 10k rep on SO, but does that mean I should be trusted more? I have used the site, sure, but that doesn't mean I am always right. Requiring those 5 votes means that 5 people have to look over the question and decide yes, this needs closing