Una Due Tfc -
Two brief points ... because I'm aware this is the Liverpool thread (apologies).
1) The value from MAN's second runway comes from the ability to accommodate high-value peak demand (peak hours slots are fully allocated in Summer months, and respectably so during Winter). Many flights using these slots would not be viable in off-peak periods. They wouldn't operate. Also, growing demand is now spreading the load more fully again following the upturn since the 2010 recessionary lows.
2) The proximity to the original runway was a necessary trade-off, sacrificing increased functional utility for a site which could achieve planning approval in practice. No good drawing up a perfectly spaced runway layout if the planning authorities won't countenance it. And the need for tunnelling to accommodate the River Bollin and the Wilmslow Road meant that the chosen site wasn't a low-budget choice.