Can only agree, specially with the odd behavior of the tree especially when you got multiple tabs open for the same manager. If I recall right the whole tree and what it opens is cookie based which in my opinion is a bad bad idea. MODx has the registry to work with the tree and could store the session data there.
Dashboard is the least used feature of MODx for me atleast, it is pain in the bum if you don't have network connection and you have forgotten to disable all XHR requests it makes. never been user, always a admin. From user point of view the dashboard could be usable but no experience on that.
Maybe new tab for the tree should be introduced, it is not a bad idea that you could browser last edited resources, chunks etc... from it. The tree could easily have 5 of each simply categorized and possibility to "load more" if required.
Personally have almost always 2 to 5 tabs open when building snippets, chunks or just plain getResources call to easily see where I am going with the row chunks and to keep myself up with the naming of tpl's. I don't know how many really use the file browser, it could have own menu really and could integrate the modxSDK directly. Even with the ACE editor and all possible solutions, would guess that people still prefer true IDE's when they are developing sites and upload the files and do not directly edit the files onsite unless are really required. Like missing ftp/ssh credentials
The tree is perfect solution otherwise. If you compare how pages get cluttered with WP or Dru#¤%#¤% the tree is awesome solution with contexts and everything. It just does not make sense always.