I can understand for solid colour coats it would be alright to spray TS-13 over fresh paint but I would have thought for metallic paints it could risk causing some of the metal flakes to shift and loose some of the reflective finish. I know you said mist coat it, but then I'm assuming the fresh paint would still be quite tacky to the touch?
I like the idea of mixing some clear with the colour paint, before going to all clear, as it must give the paintjob a nice semi-candy and deep/wet finish
. I'll definitely try it out with metallics since you have good results but I'm still dubious about it.