You may want to sign up for the Hilton card. i had points that went unused for years, and burned some on the Waldorf Astoria. Unfortunately, I had fallen from Diamond to nothing, so no upgrade. But, For 40lb/night, upgraded to the club. Room was nice (not 4 seasons or St. Regis, but nice) and the lounge was excellent. We ate breakfast each morning, had evening drinks and a few nights made the hot spread dinner after a big lunch out. We were able to walk to everything we wanted to see, with the exception of the Imperial War Museum.

Of course, you could make London your splurge, but we found this a great way to spend 5 nights extremely cheaply but still very enjoyable.