Okay, boffo stuff going on here, really. If you're a real .NET developer, have taken a Ted Pattison course, or if you generally have a clue, maybe this is really basic information is not new to you. Here it is... Hold on everybody...
The lists (and libraries) you see within the SharePoint Designer "Data Source Library" are based on automatic queries that SPD creates to display the lists in the first place. If you want to add your own queries to the data in these lists, you must use the "Copy and Modify" command within SPD.
"Copy and Modify" solved my problem of not being able to select limited fields and to set the lists property's "Items and folder scope" to "RecursiveAll" so I can see all the files within folders. (Despite my 'Best Practice' advisement, people are still creating folders in document libraries. Don't get me started...)
This only took me about 8 hours to figure out. That's 480 minutes of lost Desktop Tower Defense productivity.
My life was once filled with fancy server-side scripts, but now I'm just another SharePoint consultant.