I am trying to do an audit of the files I have in Plastic Cloud to see if there's anything in there that is hogging up space that we don't need in there, and I'm not sure exactly how to do that. What I have in my local workspace is not the same as what's in the cloud (because of ignore lists, if I'm understanding correctly?) so is there any way I can view what's in the cloud, or am I thinking about this all the wrong way?
The working copy downloaded in your machine is just the last version of the project, but the cloud storage includes all the history of the project (every previous revision for each file in different branches...)
From the branch explorer, you can right-click any changeset and select "Browse repository in this changeset". This way, you can check the tree of this specific changeset (including file paths and file sizes).
There is a recent feature that allows you to arrchive old file revisions in the cloud and this way, reduce the database usage. Please check: https://forum.plasticscm.com/topic/21799-trimming-to-reduce-size-of-the-database/?do=findComment&comment=45397