Add to the list of + factors: Completely non-smoking hotel, a rarity in Vegas.

For those with allergies this is more critical than you think as I have often found smoke drifting into my room through ventilation systems and from hallways at other 4* properties. The bar (and maybe part of casino floor) are the only places you can smoke at the Westin so you can avoid the stench on your clothes, at least until you hit the next casino.