It would be nice if in the transfer File list view there was an option to either view all files in a flat list, or to expand all folders. I would like to be able to scan through all the files without needing to expand each folder separately.

Yes PLEASE! I came here looking for info. about this very feature. Can't believe it's not available already in such an otherwise full-featured torrent client.

It's really, really tiring to keep expanding the folders in the file list on the Files tab EVERY. SINGLE. TIME. And so irritating that one has to do it repeatedly, because the state is not maintained, so clicking on a different torrent and back again resets the list to a folders closed/contracted state! >:( Gets old real fast, I'll tell you that.

Devs can add a new button to expand and contract, a toggle

Yes, although along with a per-torrent toggle, ideally there'd be a permanent app-level user preference one would be able to set.