No, I disagree.
There are many cities which I would consider "once only" destinations, including Paris, New York (actually once was too much!), Detroit, Los Angeles, Miami, - and London.
Generally you've got to have a reason to visit a city more than once - perhaps, as has been alluded to, football - which the Northwest certainly has in it's favour.
It's not necessarily a question of being "anti Manchester" so much as being interested in visiting new places.