I don't delete any houses, just all the houseboats (but the one I want to play and the ones I leave on problem ports and make No Visitors Allowed). I do move everyone to a house on land.
I like to redo homes and turn the bathtub around normally, set the front door, and just get rid of the problem areas (like the stacked spiral stairs and the stairs to the fountain in the park).
It's a wonderful world and I love playing there without any lag.
I do remove the resort towers for the two expensive resorts and things that spawn NPCs.
I also give all the townies cars and boats to cut down on taxis spawning.