Closest I've come to spraying the wells was having the rear ones on the Tahoe done with Wurth's stoneguard stuff (forget the actual name, had my Audi dealer do it while it was in for some paintwork. It's held up well with just a bit of wear in the most vulnerable areas. I maintain it with FastFinish though I might use up my old Armor All on 'em.
I'd be scared to spraypaint such stuff for fear of overspray. No matter how careful I was....
So what I do is: smooth and painted- just treat like the rest of the paint; textured and painted- IUDJ, maybe some BIS, maintain with something like FastFinish; plastic- FastFinish and where they're worn...eh, I just let 'em look crappy (the FastFinish helps a *little* and I say "good enough"), never get around to ETRing them though I did use it the "splash shields on the Tahoes front wells (but I've yet to reinstall them so I can't say how it holds up).