The SPG 4 PM checkout for Gold and Platinum is great. I have never been able to get anything after 2 PM with IHG or Marriott (as Platinum on both). SPG Lifetime Platinum is pretty hard to make so I am working toward lifetime Gold.
I agree that Marriott should make Platinum benefits better. The UA thing is great for those who don't have status on UA but worthless to me as a UA Lifetime Gold.