To chime in, I think just about every Mk3 I've ever seen is missing at least one of the door lock bezels. I believe the retaining clips on the back side fall off inside the panel or otherwise break. Was just gonna glue mine on, as there's nothing structural there, but I'd be happy to buy a set that actually work as intended.
I'd also be happy to buy a nice looking set of kick panels. The mounting tabs on mine are crap, so they don't like to stay in place. I like the back lighted LED idea, would be fun, but the only good way I can think to make it work would be to tap into the courtesy lights' wiring.
If I come up with any ideas that 3d printing would be suitable for, I'll let you know.