Have you tried the toggles on the toolbar that turn off display of all waypoints or all tracks?
Yup, that's useful, but I have to give a thumb's up to the OP's suggestion of an "ALL-ON" or "ALL-OFF" toggle for the loaded files. I would actually like to see this expanded to include "Unload All", "Unload Selected" or, for that matter, an "ALL" option for any single file operation. Of course I'd like to see some safeguards built in like "You are about to unload File.GPX, are you sure?" But that will still speed things up a lot. I usually end up with a BUNCH of recent files loaded and it would be nice to be able to
(1) Select all
(2) Deselect a few
(3) Unload all selected
This is strictly an interface issue, not a function issue. All of this is doable now - just one file at a time.
KenF