+1 to use and auto-connection of each of these given the specific constraints. Each covers core and expected functionality for this snap and the UX would suffer without them.
It sounds like this is required because of the lack of UI (i.e. the UI did not need access to this file and used polkit as I recall). Once the UI is back (which sounds like is in the works) this will not be necessary. Does that sound accurate? I will assume so until corrected.
The UX of automatically connecting the personal-files interface to use the snap login token is poor. It means the UI will magically be showing private snaps or not, depending on whether or not the user had already run snap login. This is in contrast to the polkit integration, which would force the user to login in right then and there order to see such things. In this way, requiring the connection of the interface seems similar.
Beyond this, though, it looks like the level of access provided by polkit and that provided by snap login are not the same (it seems polkit has less). I agree with @jdstrand that it would be a bad idea to set precedent for accessing this file automatically. +1 to using personal-files to access the token, but -1 to autoconnection.