something you really should try is oil paints,
and I mean the ones in tubes !!
you can thin the oil paint with ...wasbenzine(dutch name)
(don't know what it's called in English, but you use it
to degrease and remove tape residue and evaporates quickly)
you can thin it to a really thin wash, then apply it all over the model, as the thinner is diff then the one you used for
normal painting, it won't dissolve the paint underneath !!
after it dries you can wipe the top layer off with brusher or
a cloth, and leave the oil paint in the recesses, the oil
paint takes a day to dry and can easily be removed and changed.
if you use a mat paint layer as a base you can really make a
surface look old and worn as much as you want, when using
gloss you can wipe all of it away and just leave it in the recesses.
just try it, it won't have to perfect first time, because
you can just wipe it off and start again
I used it on the model in the pic
if you want I can make some pics to show you
Xeno