Cats can spray base boards or sheet rock.

So I hose off my outdoor condensers' fins and spray for ants and have been changing filters for my tenants every few months.

If the switch is white you can just spray paint them.It depends on what kind of rental you have with what they expect.We have small old water stains from previous leaks on the ceiling when tenant moves out.I buy a spray can of Kilz for 5 bucks and usually last about for 2 of my apartment units hitting spots.You can't tell afterwords with the ceiling and it looks great.It's cheaper than scraping popcorn and trying to match or scraping the whole ceiling and a flat ceiling because it is old showing all imperfections if you just scrape and paint it.On the light switches I agree it works to replace them all but in older apartment buildings I try not to do that because what I have found is the wiring in behind is cut short or has too much excess crammed in.So if the wiring was all clean and the right slack from out of the box it would be easy to replace.I have found that some go smoothly and the others are a bit of a pain to change out making adjustments.The Kilz for the ceiling I only do that on non-active leaks where the drywall still has integrity to it and is not sagging.If it is sagging I cut out and put a patch in and then popcorn over it after priming to stick.All my tenants want is a nice,clean place to live.If you have a high end tenants paying premium bucks then finish level and what the tenant expects will change.In mine replacing everything will only net me maybe another 30 bucks a month in rent and the thousands spent will take 5 to 8 years to recover if everything goes perfectly with each unit.

At some point in the near future I should have some case law to support that opinion, so take it with a grain of salt, consult with a very good securities attorney, and remember that I'm not an attorney and don't give legal advice so feel free to ignore everything I just said

No one can predict what can be sold so I would take that statement worth a grain of salt.

Can I just spray foam the cracks in the ground with an epoxy or foam?

We had the guys re-float all the walls and spray new texture and it looks great but I've also heard of guys painting directly over paneling.Anyone done this with success?

Take it with a grain of salt.

I can't imagine that smearing glue would be any quicker than using zip ties, unless the glue is in a spray can.

If you discover multiple layers of plaster and/or no insulation I would budget a reserve to gut each apartment back to the studs as they turn over and insulate {We've found spray foam to work best in the older houses, especially if they have rough-cut framing and sheeting}.I am partway though this process with one of my buildings that is 120yrs old ... only I am stripping all walls back to the studs and dropping the ceilings as well.