Your take is a good one - the bathrooms at the MO are outstanding and the 4S really feels like an oasis in the Vegas-ness of Vegas.
One thing you didn't really cover (in this post) is how good the MO bar is. The atmosphere, views and leggy staff are really great. Not sure the 4S has really anything to match it -- much like MO doesn't really have anything to match the outdoor dining at Verandah.