Text layer hasn't full range of details, it's organized into two levels (page and line), while OCR engine on  IA servers produces a very rich "tree" (page, column, region, paragraph, line and word). Images can't be finely tuned, but it is possible, given images of the same width/height of better quality, to "transplant" text layer into a different djvu with a few DjvuLibre commands.

Is anyone of you interested into a rather deep exploration of djvu text layer by python? I'm working about it, but I feel that there's so much  to do, and  so much to gain. I'm currently working into a Windows dropbox folder, containing DjvuLibre routines too.