One of the main reasons I don't post on BP as much as I used to is that someone is always "wrong on the internet" and it takes too much time to refute all of the nonsense that gets sprayed around.  

Hard as i try though I just can't make that activity fullfill more than maybe 10-20 hrs/week, and it never feels like work anyway.How I miss going home exhausted at midnight after a 16 hr day...the sawdust on my face...plumbing that sprays at me....bitching at my contractors on a daily basis....even all those visits to Home Depot.

Can I just scrape it all off and re-spray it with a finer textured spray?

try getting a primer called gripper by gliddon and after cleaning reall good spray that primer on its verry tough then try spraying on a glossy white oil paint also verry tough I think it will last along time I did this to my pink tub and it seems verry durrable so far, cast iron tubs are much better than the thin sheet metal ones.

A texture spray gun on sale for $25.99...This is a rental house.

I personally wouldn't do it if its truly major rehab.You could damage their personal possessions with dust, spray, debris etc...They might not have a functional living space and you are responsible.Also, based on my experience, unless its super simple, "shouldn't take more than a day" typically turns into 2,3,4,5 days depending on the age of the home, and sometimes a part just isn't available at the home depot and supply houses are closed on weekends and online expedited order says 48 to 72 hours and you go..."

A few days later over the weekend someone broke into that house and smashed all the drywall, the kitchen, the bathroom and spray painted the walls with the exact same phrases that the illegal dumpers were using while yelling at my workers so it was pretty clear it was the same guys.

I put spray foam insulation in the cellar along the bands and maybe even in the joists (can't recall) and it made a huge difference.I would also look at the type and quality of your HVAC systems.

Spray paint them into the driveway.

I explain that they are responsible for light bulbs and small stuff, like the occasional ant spray issue (I usually leave a can of ant spray at the property), and I tell them that we do inspect the property, will give notice as in the lease, and that they can leave a list (one tenant leaves post-it notes all around the unit) if they see any minor fixes they'd like taken care of while we're there, which eliminates most of the stupid-trip calls throughout the year.