Personally I'll still go to the cities I want to see, multicultural doesn't mean that it's all the same - cities will still have their own culture and unique feel to them regardless, they'll just incorporate more and more influences. Or let's put this another way - Glasgow and Edinburgh, two cities in the central belt of Scotland, split up by a difference of around 50 miles but the cultures are pretty different, if they were monocultural (which is what you appear to be advocating) then they'd surely be pretty much the same in feel and they are distinctly not.
What's a classic Englishman? Bowler hat, pin stripe suit and umbrella - the archetypal city gent? Or a proper Cockney geezer? Or something else entirely?
Whichever the answer is, if people are coming to London purely to see classic Englishness then they've obviously not quite come to terms with the fact that London is now a global city and as such has people from a vast array of countries in it and is richer for it. If you want to see typical Cockney market stalls then you can do that, you might have to search a little bit harder but it's perfectly possible, same for seeing city gents in pin stripes and carrying umbrellas.