The Idaho house will be torn down. I think it's a good idea. It won't stop some people from "visiting" the site, but it may keep the numbers down.
Some people have a fascination with especially gruesome crime scenes and the house where 4 college students were stabbed to death in Idaho certainly qualifies.
I was talking to our local news guy here and I believe the house where the murder of Jane McManus took place in 1977 was torn down. He wasn't sure.
Even if you don't believe in "hauntings" or "spirits", the IDEA that they MIGHT be real, or that other people believe it, can strongly affect your imagination.