I've been going on the original starter with my car. My Tempo starter lasted all its life until the bearings wore out and the thing started to seize (which is why I swapped back in the original starter for my car). Starters wear out much faster the longer they have to crank an engine. My engine starts with about 1 or 2 seconds of cranking. Still, I've never personally replaced a starter on an Escort. If they keep having starting issues, try pop-starting.
If the brushes are wearing out, you're getting cheap ones, that are using cheap brushes (they won't spin as well, either). I have an original '85 Escort starter here that was installed on a Tempo to replace its original one since the previous owner couldn't get it to run properly (the engine had crumbled pistons and no compression), so he kept cranking and burned out the original.
However, our starters are completely rebuildable. Bushings, stators, rotors, starter gears, brushes, are all replaceable. The other option is to switch to a Tempo style starter. It's smaller, not as rebuildable, and has the starter relay built on. You could scour junk yards for a bunch of 'em. They come on '88 and later year Tempos. Otherwise they have the same starter as an Escort. I think that would be cheaper than spending money on rebuilt starters from somewhere.