I like the "Reuse existing TAB" because I frequently open lots of files, following a Search, but modify very few. If I set Open-in-new-TAB I then have to close lots of TABs.
However, sometimes I do want to "keep" a file TAB, once opened, rather than reuse it.
So if there was a way of explicitly indicating "Open in NEW tab" I think that would provide ultimate flexibility.
My suggestion (Sorry @Dan, hopefully clearer this time) would be to allow RightClick on Search File-list, and have an "open in new TAB" option.
An alternative would be to RightClick the TAB and choose "Pin" or somesuch, which prevented it being reused, and thus double-click on next file (in search file-list) would then open a new tab (and then reuse that TAB for any more file-open commands)