I know what you mean. But having said that, I think the formula works well enough to justify another couple of movies. I mean, having pretty much the same formula hasn't hurt other franchises like Halloween or other slashers. But they could shake it up a bit. I think ditching the humour might be a good first step. Have an opening kill survive the killings, have one Ghostface killed in the opening and another one to be tracked down during the movie itself - small tweaks like that might help. In terms of motive, they need to lose some of the ones they've done, such as a family member of Sidney's. Maybe just a motiveless killer who wants to kill the "unkillable" final leads of the previous movies. I think they should stick with the main cast, just shake it up and maybe kill one of them off.