If all we wanted to do was Manned Mars, what you say has some merit.

But if we are to look at the big picture, I say there are two reasons to go into space.
Reason One: Space is like the Earth's Ocean- it's important in terms of miltary uses. There is a lot to say about this, but this is mostly concerning space near Earth- at least in terms of the first part of 21 Century.
Reason Two: Energy. Both environment of harvesting and transporting energy.

Space is near everyone on this planet [it's 50 miles up]. Halfway to space [starting 25 miles up] vehicles can travel up to a distance of 12,000 mile in less than a hour {at about 6 km/sec}. Travel anywhere on the planet in about an hour. You can't do this if you only go 6 miles up [what is routinuely done in air travel]. You can fly at about 2000 kph at about 11 miles up [Concorde].
Hmm. "Concorde travelled, per passenger, 17 miles for each gallon of fuel (mpg)... This is comparable to a Gulfstream G550 business jet (~16 mpg ...), but much larger than, say a Boeing 747-400 (~91 mpg ... per passenger)."
http://en.wikipedia.org/wiki/Concorde
So, if a Concorde travelled 3,400 miles each passenger would use up 200 gallons of fuel.
Anyways traveling in near space or space [assuming the technology is somewhat mature] could probably allow using less fuel [not including oxider] than Concorde or Gulfstream if one is traveling more than say 4,000 mile distance [and you would get there in about a 1/4 of the time].

Anyways in regards to the Moon. First it has a vaccum- this useful. Second it probably has minable water. And most important it a has low gravity well, which mean stuff can shipped off it's surface at lower energy cost to anywhere in Space including near earth [or even possible to anyplace on the Earth's surface- not possible in near future] in comparison launching from Earth.
The problem with the Moon is it's a high theshold in terms of start up cost. That problem can be solved- I've endlessly explained how this can be solved.
But as an example of what would NOT be a practical way to solve this problem:
If govt decided [for whatever reason] it wanted a huge amount of solar panels in space for a big SPS. Making solar panel on the Moon and shipping them to Earth orbit could be cheaper than making panels on Earth and shipping them into space. Another "way" is that if govt decided [for whatever reason] it wanted to actually start a colony of Mars [or Mercury/Venus] so the magnitude of this project is around +100 people as a population, and several of trips per year for decades of time. If the Moon had minable water they would be fools not to mine this water [more significantly they would fools if they did not permit the private sector to mine it and sell to them at cheaper cost than what they would spend shipping it from Earth].

The point I'm making is that if we ever do anything serious in space OR if we merely plan on continuing playing around in space for any long period of time [which is a given because of Reason one and two {if miltarty power or Energy needs are not important in the future then I guess it's not a given} Then the Moon should explored and exploited. And if America doesn't then some nation or someone will.