I may have a quite different bias than you, and I'm certainly an outsider on your local politics, but I don't see how infrastructure development can hurt. Geography plays a massive role in economics--you can't change geography very much. But you can improve routes (infrastructure) between trade centers and (if you believe that trade benefits both parties, as I do) make improvements to local economies based on infrastructure improvements.
Put more simply, consider ticket sales at Goodison: if there were a rail stop closer to the stadium, ticket sales should increase, simply due to ease of access, without any change in demand. (Similarly, if you removed the roof supports obscuring view...).
No doubt the Northern Hub would help Manchester, but trade is not a zero-sum game, and improvements (unless they were only in Manchester) should have big effects for surrounding areas.