Mars could return dividends at the same time that Luna does if they join forces.
Luna has considerable potential for manufacturing and shipping goods into orbit about Earth where it can be of financial benefit, but Luna is short of Hydrogen, Nitrogen, and Carbon. These elements are not only necessary for life, they are useful for many industrial processes. Mars has all of these elements in reasonably recoverable concentrations, and could export them to Luna and Earth orbiting factories.
Mars to Luna Transport
The cost of lifting items from Mars could become considerably less than the cost of lifting them from Earth. Low Mars orbit, at an altitude of 100 miles, has a velocity of 3440 meters per second, less than half of the velocity needed to orbit Earth at that altitude, more than twice the velocity needed to orbit Luna. With reusable rockets built on Earth to use liquid methane and liquid oxygen, if the exhaust velocity is 3500 meters per second, there should be 36% of the take-off weight in orbit. With wings for a supersonic in ground effect landing in the 0.1 psi Martian atmosphere, the empty weight should be held to 30% leaving 6% of the take-off weight as cargo.
- There seems reason to believe that supersonic in ground effect landing is a significant problem, and that it should yield to the proper effort, resulting in an economic Mars to Low Mars Orbit Shuttle (MTLMOS pronounced metal mos to rhyme with verbose). Donald Campbell was killed on the 4th of January, 1967 when the "Bluebird K7" racing boat flipped over and disintegrated at a speed greater than 300 mph.  The problem seems to have been longitudinal instability when high ground effect lifting forces acted on a center of lift that shifted rapidly with changing attitude.
- This sort of problem is made more difficult by the need to consider the reflection of shock waves in supersonic flight in ground effect. Such problems were handled successfully when the "Thrust SSC" broke the speed of sound on land during a 15th of October 1997 setting of the world's land speed record. 
- An ordinary wind tunnel by itself is insufficient for testing craft in supersonic ground effect conditions. A moving belt of caterpillar like treads on the bottom of the wind tunnel moving as fast as the gas in the wind tunnel could simulate the runway rushing past during landing. Having a belt of treads that are broad enough and move fast enough for the simulation would be expensive, but not as expensive as doing the testing on Mars. At least with only 0.1 psi of carbon dioxide needed for a simulation, it would not cost as much as otherwise to fill the wind tunnel with cold carbon dioxide.
A skyhook is an interesting alternative both for Luna and Mars. Probably, it allows even more cost reduction.
If the technology for the supersonic in ground effect landing is not ready soon enough, there is the possibility of mining Phobos. Phobos may be rich in volatiles, which are needed by Luna. Phobos could be ground up and processed at one end and the tailings dumped at the other end. It should be many years before the entire moon is converted into tailings, during that time Luna and Earth orbiting factories should be churning out a great many solar power satellites, orbital habitats, and orbiting space ports to help lift traffic from Earth. If Phobos is 30% by weight volatiles and ships six thousand tons a year that is part ammonium cyanide and part propane, then after fifty years 100 billionths of Phobos will be processed.
Initial Martian settlements will have little industrial infrastructure, and will have to import many goods such as electronics and medicine. Lunar settlements are in a good position to supply these needs, as the energy cost of transport from Luna is much less than from Earth.
Like Lunar settlements, Martian settlements need funding to survive. Sales of Martian resources to Lunar and other interests could be a major source of cash.
Luna to Mars Transportation
|This section of the article is incomplete or needs more detail. You can help Lunarpedia byor correcting it.|
Settlements on Mars and Luna share many needs and opportunities.
Information such as patented ideas, literature, scientific research, and computer programs can be created and traded between Luna and Mars at little to no transport expense using a radio link.
- Bluebird K7 article at Wikipedia
- Near-Infrared Spectrophotometry of Phobos and Deimos http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002Icar..156...64R&db_key=AST&data_type=HTML&format=&high=452a3fe65704274
- Phobos weighs 1*10^16 kg according to the Phobos article at Wikipedia.