Full agree with OP especially the last argument.

The excuse that pretends instancied houses are ressources consuming have always sound to me like a bad joke. Any Inn room already works like as an instance and guess what : one character can't be in two instance so it wouldn't change anything. SE excuses are really, really poor excuses. The worst : we can loose seasonal event items if we loose house and never getting them back since no PNC sell them, even thought we have the achievment.