The walnut burl and curly maple on this one are .025" veneer. Aside from the difficulties of cutting it, I haven't had any problems in the 6 months since it was assembled. I haven't allowed it to dry out, but it has seen up toward 70% humidity on a few rainy days, with no finish on it. It's all glued down with LMI white glue, no CA. Inlay on headstock is the same maple, also with no problems.
I was very careful not to touch it until final sanding time though, and it has the deeper purfling line borders to fulfill the practical purpose of the rosette of catching any cracks that may form at the soundhole.
Next time I'll probably glue the good veneers to another layer or two of veneer, something plain and cheap, simply to strengthen it for cutting. Maybe alternate grain to make a micro-plywood
This one I ended up cutting the maple stuff with a dremel router, as I couldn't avoid breaking it with a jeweler's saw or X-acto knife. Walnut ring was just X-acto knife, first to rough it out, then slicing lots of slivers off of it while checking fit. Probably wouldn't need to bother with a second layer on that, as it was pretty easy. Big, so not too delicate, and didn't have to be perfect since I'd be routing off the edges of it for the purfling lines in the end anyway.