You might not want to switch hotels, but it's worth considering the Indigo Tower Hill for the two free nights and sightseeing the Tower of London, the Bridge, Greenwich, etc. from there.

Then move to the Indigo near Earl's Court using points. It's probably the best value IHG hotel on points in London - 30K per night - and a short tube or bus ride from Harrods, Hyde Park, Buck House and the west London museums. I find the various Holiday Inn options to be quite depressing and in need of investment, although they do have the advantage of location.