I don't think that it really makes any difference, Gary. With mostly open grid benchwork, I had to do the basic landforms first (plaster over window screen), and that was given a coat of thinned paint to diminish the "fresh blizzard" look. I then used a brush to paint all of the rails: this goes pretty quickly and is a good job to tackle, in stages, when you don't have enough time in one block to really get into a big project. In my opinion, painting the rails, followed by ballasting are the two improvements that give you the most visual "bang-for-your-buck", and for the least investment in time and effort, too. I ballasted first, although there were several areas where the fill and sub-ballast had to be installed along with the ballast, and that just naturally segued into the lineside scenery. Unless you're modelling a Class One line, with manicured ballast edges, there's always going to be areas where the ground cover creeps into the right-of-way, and places where the fill and ballast tumbles down an embankment to mix with the weeds. And secondary lines can be somewhat overgrown, and sidings: well, the "ballast" is more ground cover than true ballast - doing both the track and the immediate surrounding area ensures that there'll be some continuity of colours between the two. There aren't very many "finished" areas on my layout, but except for the Highline through Dunnville (awaiting backdrops) and the grade to Park Head (awaiting the screen and plaster) all of the track and most of the immediate environs were ballasted and sceniced at the same time.
In the photo below, so much glue/water mix ran down the hills that the trackside scenery inadvertantly spread out some distance. I thought it best to not let it go to waste, so I applied some ground foam to soak up the excess. When I finally get around to finishing this area, most of it will be covered in trees. Both bridges are removeable, and I'll be doing the "water" first.
The mainline at Port Maitland, which runs through the GERN complex, is all on plywood, with no cork roadbed, so I had to simulate the sub-ballast by spreading cinders alongside the ballast edge, and that just naturally flowed into the groundcover.
At GERN itself, what little ballast there is is mixed with dirt and weeds, along with quite a bit of spilled flux.
Most industrial sidings have more ground cover than ballast, and with the relatively narrow areas between tracks, it's easy to do the whole area at the same time.
Wayne