I find that using the wheel button to click a second or subsequent tab closes it (in the manner of Firefox) and that's very slick. Would it be possible to make it so that clicking a folder with the wheel button opens that folder in a new tab?
Edit the All Folders filetype and set the mdblclk event to run Go newtab (or go newtab=nofocus if you want it more like Firefox). Then when you double-click a folder with the middle button it will open in a new tab.
You can't make it do this with a single click, only double-clicks, but single clicking with the middle button already performs a useful roll (it is like ctrl-left clicking, without having to hold ctrl).