Having a number of trees in various stages of presentation, I decided to have a bit of a re-furb. this included adding Lichen to tree armatures and spraying some of my 'loo brush' type trees with glue and rolling them in turf flock.
A picture and some discussion is over on the blog LINK
http://battlefieldswarriors.blogspot.com/2018/08/tree-building.html
An interesting read. I have also been sorting out and increasing the number of trees I have, all commercial, but your ideas sound very good for increasing the bulk of foliage.
Good stuff, Norm.
Cheers - Phil