"Policing the world" doesn't have to cost that much. Nearly $2tn spent just on the pointless Iraq misadventure. How much public transit and education could that have funded?
Policing the world is a jobs program for all of the unionized factory workers at lockmart and Boeing that would otherwise be, at best, trades workers earning a more modest wage. We can thank the MIC’s placement of factories in strategic congressional districts for that
The entire NYC subway, the busiest system in the country, has 660 miles of track. NYC has a GDP of $1.3tn and the subway system has a big hand in making that possible. So that's actually a pretty good RoI. It'll go a lot further (haha!) in a less expensive city.
But that also goes back to the original comment about spending the surplus wisely.