I don't think there is anything wrong with that. I don't have a big house with a spiral staircase and white carpets, so I sometimes fantasise about that Doesn't mean if I was given the opportunity I would have that (especially given how clumsy I am) If you can say the same about your little fantasy, then I am sure it wont cause any harm?

Also if this is just a fantasy and not attached to anyone real then I don't think it is disrespectful to your wife really. x