My Add-on Install & Upgrade add-on allows you to install/upgrade multiple add-ons with only one cache rebuild.
So you could either select a load of ZIP files which will then be extracted and copied across, have the XML files imported and finally do a single cache rebuild. Or if you prefer to upload the files yourself, you can do that bit manually like you normally would, and just upload multiple XML files which are then imported and finally a single cache rebuild occurs.
Suggestion: Add a 4th option for Install/Upgrade, enabling you to point to a directory patch on your server where you have (ftp/scp) uploaded a bunch of add-ons (either .zip or unzipped in sub-folders) and all within will be actioned from there. Scenario: you upload add-ons to your server and install in dev environment for testing, and then once a week/month you will upgrade/install several add-ons, sort of like "patch tuesday" type of methodology. Since I'm already uploading on to the server for dev, then I don't need to upload again.
The directory tree would be like so ...
-> xf/
---> styles/
---> library/
---> add-ons/
------>completed/
---------> AddOnInstaller-1.0.0.zip
---------> Change Thread Starter 1.0.1.zip
------>todo/
---------> AddOnInstaller-1.1.0.zip
---------> addon-Waindigo_JoinUserGroup-1.1.2b.zip
---------> FoolBotHoneyPot_v2_2_13/
------------> upload/
------------> addon-FoolBotHoneyPot.xml
---------> GritterNotifications-1.6.2.zip
[ ... etc ...]
I would point the add-on installs location path at "add-ons/todo/" and it would process all within, moving them to "../completed/" when successfully completed