Yes, sometimes I compare because you are absolutely correct about London prices as well as the weaker dollar. It's hitting hard for all the time I spend in the UK--but I still do it.
For Hilton, honestly I look more at the reviews for anyplace in my budget because every hotel is hit and miss, it seems.
For reference, for my trip it was either HH or Marriott points, but I have more HH so I am holding the Marriott ones for another trip. Conrad cash rate for my stay is £321, Trafalgar is £446, mine is £245, but the hotel is newer and has the higher rating on review sites than others in my point range. Also, with Hilton, except for a few business rates, most of the best rates are nonrefundable, and I also try not to book those since I often do change where I want to be. I figure using points in an expensive city is still worth it for me to use points when I earned them almost passively--meaning I was going to live in some hotel for several months, so it's nice to use them. But I'm not paying 100K a night if I can find a hotel with 60-70K a night when both have similar amenities and are close to transport.Definitely ready for our dollar to improve...