I am considering switching a heavily developed site that is currently yoo/warp to rocket/gantry.
Would I need to install the full files (rocketlauncher?) over what I currently have, to be able to switch frameworks, or is installing the template sufficient?
the rocketlauncher is a full joomla install which will give you an exact copy of the demo site.
so it can not be used on an already existing site.
i suggest that you create a copy of your site on a test server (use akeeba backup) and then install the template of your choice either from the template bundle (template + gantry framework) or use the template standalone and the gantry framework seperately.
also make sure to download the extensions package for the template you choose and install all the contained extensions.
then you can reassign all the modules (gantry templates use module positions that have different names than the module positions in other templates) and once you are all done you can move that copy to your live server to replace the existing site.
May be it would be worth mentioning that the warp-menu is coded directly into the yoo-template and not a standalone module so it cant be used with gantry-templates!