I like mountains. I've about 25 linear feet of them most with tunnels and all open inside. Originally I started using aluminum screen wire with hydrocal, and it just took too many coats or the use of paper towels in the mix, which makes it messy. Now I use Woodland scenics cloth which is SO EASY to use. Now I must tell you that I DO USE FOAM as a profile board upon which I fasten the screen wire to. Originally I used drywall screws to hold the screen wire until the plaster dries, but now I actually cut the profile out of lightweight foam, then trace scraps of 3/4 plywood with the shape about 2 inches wide and glue and screw it to the fram so I have something to staple the foam to.
I've also used foam as a flat base for scenery only because it is lightweight.
Stacked foam typically looks like stacked foam unless they put plaster cloth or ALOT of sculptamold on top of it.
I do want to give credit to those very talented people who can and do make nice looking layouts with foam and little or no plaster, but for every one I see that is nice, there are 8-10 that look like stacked foam or worse.
One side of a set of my mountains
Just my 2 cents, trying to learn to be a model railroader.
Course there is more of my views on scenery and foam on my blog.