What are efficient solutions to prevent a huge amount of panes in a Panel?
Panels have "varients" with selection rules.  You can set up which variant is triggered by which value in the url variable that you named in the path setup.  This way, you can have your pane layouts not get so cluttered with options that are only visible a fraction of the time, but still have the same capability.  Either way, the check for display is a growth order of O(1) so not that much of an efficiency concern.  The views would be a better place to increase efficiency, set a limit and a link to the full list in a footer.