It's a traditional area. I am not convinced from the locum work I did there (late 90's) that the quality is any better than elsewhere. You are paying for a name. If you want to know who to see (ie best) then that is very dependent on what the problem is etc.
My experience too. I have a number of friends who are consultants, a couple work on Harley Street actually, but if me or my family need a consultation I tend to connect with friends and ask them to source the best person in the given area. It's quite amazing how often 3 or 4 come back with the same names, down side is they can be all over the country but the really good people doing the really innovative stuff tend to be known in my experience.