I have used Kagi for several months now, and I find that the ability to decide which searches I want quick answers for to be useful. There are certain searches where I feel comfortable with accepting a quick answer, and others where I don't think it would be useful. Being able to avoid the clutter unless I want it is nice.
I don't really web search for those things but I can see why that would be useful. There is a feedback site that they are very responsive on; you should post there if it hasn't been posted yet.
Re: bangs ruining suggestions: you can put the bang at the end of the query instead of at the beginning.
