I have thought of most of those things.
Maybe not thumb tacks but something similar. (All the best ideas were stolen by our ancestors)
I actually have some plastic track, but it is is set up for glass and I thought it too narrow for 3/4" thick wood doors.
I considered Formica glued into the grooves.
I miss-figured one door and glued a couple of thin pieces of oak on the bottom and its sliding better than it's brother. I am thinking about thin pieces of very dense very hard wood, Maybe Osage Orange on the bottom of both.
I think a very small amount of sanding dust and maybe grit has gotten into the tracks, I will clean them and sand them into submission.
This is something of a Mid Century Modern piece. Maybe I should have used barn door track.
Thanks for all the suggestions, keep them coming.