I think there is a lot of wasted area. The search field could be in the same line with the results value and dropdown menu for filtering. And at the left side to the current results is also too much white space. A little bit on both sides will be okay, but not as much and static as it now is.
I am having trouble understanding what you are trying to say? Perhaps if you had a visual mockup of what you are proposing?
The search page should feels more dynamically, well sorted, and more like a Google Suggests or other good search engine’s web page.
For what it’s worth, Google search results pages have even more whitespace (a narrower column) than Discourse. Keep in mind that the wider a column of text is, the more annoying/difficult it is to read.