slapinfunk and I havent stopped at one in the past couple of years... but they were closed for "remodeling" and now have reopened. Frankly, I dont know about maintenance. The lavatories as I remember them were like those found in stadiums and arenas, and I doubt that with the current budget they are staffed. I doubt there are vending machines because they would be ripe targets for theft.
my tips: Barstow-- plenty of fast food joints and the Chevron station right off the 15 has clean rest rooms and refreshments. Very nice. Best accessed if travelling north. For southbound-- there are the truck stops with the McDonalds next door. The truck stop next to the Mcdonalds is VERY well maintained and very clean. also refreshments.
Victorville is not a "driver friendly" as it used to be. the chevron at Baker is Ok for a quickie if you have to.
the casino at Jean, and the casinos at State Line primm are always clean.