I stayed for 5 nights in December. Cash stay. Diamond Ambassador.
Got a nice room upgrade from base room to a 1 king bed suite, high floor, nice views.
Free breakfast - any dish from the a la carte menu, and one extra side (eg bacon). Unlimited juices and hot drinks.
Kimpton password is a lucky dip. Two of the choices were a free room upgrade, and a Kimpton candle.
Overall was happy with stay.