I like the look of ballast, but after ballasting/glueing my Atlas O track, vowed never again. What I did was arrange my track on my 1/2" foam board, then used a section of 3/8" plastic hose to lay up against the ends of the ties. I then used a Sharpie and drew along the outer edge of the tubing. Removed tubing and track. Painted a wet coat of gray (or whatever), then sprinkled O ballast into the wet paint - kinda like we used to do with green sawdust for grass. Vacuum the excess and screw the track into place. Without staring at it, the looks are convincingly real. Don't have my phone with me right now otherwise I'd post a pic.
And, yes, I've changed the layout a bit; I just take a small section of Atlas O track, right side up, and scrape the old ballast using the ties as a scraper. Doesn't gouge the foam like a scraper or putty knife would. Vast majority comes off; what doesn't I'll just use a bit more grass on it.
