@ciane Yeah, I converted one nice looking lot that you had changed to no visitors, but which had been that one modern looking resort with the tower into a residential lot, and built residential apartments on it. Every day a large group of sims just arrived and walked into my house making themselves at home. I also noticed while I was landscaping and building, I was getting the little plus signs when I put things up. I thought it was maybe just that, until I tried having someone live there. I figure it should work normally if I totally bulldoze the empty lot and replace it.
I killed them with MC because I've never seen a sim in-game attempt to go to work, nor have I ever seen a heavily pregnant sim (she gave birth the next day) capable of working out at the gym on a weight machine. I don't know if it's just her or if I just haven't noticed it with NPCs before but as I'm just kind of testing the world (once bitten and all that) I thought I'd get rid of them to see how it worked.