I believe the NY Times reported the returns were 11%, not 18%. Regardless, every year we see teams with mid-range payrolls in the playoffs. Spending is not The Answer. Good scouting and smart spending are The Answers. It is proven each year.
Spending by itself indeed is not the answer. The Mets themselves taught as that in 1992-3 and consistently throughout the early 2000s.
But neither is stocking your team with players from the thrift store. At some point, you gotta spend money to win.