yeah. I finally stumbled on the "writing extensions" part of the wiki, and the scales were lifted from my eyes. A mention of that tutorial in the SmartDashboard ScreenSteps or the video tutorials would be appropriate, hopefully one of the really clever WPI people will see this
Need to look at the code for the Textbox widget to see how changes get reflected back (looks like they rely on the Swing ChangeEvent). If I can adapt a JSlider or JSpinner as a POC (making the editable property work, which looks straightforward), then we're home free; once you've done it once, the variations are relatively easy. It just looks like a few hours work, need to find the hours.
As a professional Java developer, I gotta say the SmartDashboard is a slick piece of work. I tore into Team 341's 2012 DaisyCV, and a lot of things are getting *very* clear.