My business partner brought one over and I just sprayed it on the wall and didn't even scrub it.

Youll never have enough spray foam and caulk for houses this old.

If it's really spoltless and clean, hire Orkin to do a once around spray. 

I pay monthly, they spray for insects and traps for mice.

I bought some bug spray and started cleaning.

The seller offered to split the cost for termite spray and we got the house treated last week. 

I had this problem with a poorly built house... it had vinyl siding and they had gotten the drip caps wrong around the tops of the windows and doors and also forgotten the spray foam.  

If your in a real sandy enviroment, or they spray a lot of salt/sand on the roads, do consider that your tenants will most likely walk in with shoes onto that immediate area- expect that area to have wear and tear.

They can spray the wall tile and it'll look like new, but looks like you've already started demo lol.

Yeah finding the slight pattern will help with the efficacy of the effort instead of just spraying offers.