Whether as a default setting, with a tick/selection box somewhere (not too much UI space there though) or a user preference, I think that there should be a way to do advanced searches from the search box.

If there is no significant performance hit from it, simply making advanced query syntax the default would be the most sensible solution.

There is currently a very simple userscript providing the same functionality: http://userscripts-mirror.org/scripts/show/123408.