Is there any coordination between governmental space agencies in order to achieve complementary science goals with interplanetary and other space missions? If so, is this done somewhat informally through the academic world, or is there some formal institution for this?
My impression is that missions from different governments sometimes overlap suboptimally. For example, are ESA's Mars Express orbiter and the ISRO's Mars Orbiter Mission really complementary with two NASA orbiters already there? Is the ESA's ExoMars Trace Gas Orbiter to be launched in 2016 really an added value to the NASA's MAVEN (Mars Atmosphere and Volatile EvolutioN Mission) launched in 2013? Would NASA have considered doing those missions on its own if no one else had? Do they fit rationally into the grand plan of Mars exploration? ESA has also followed NASA to Venus and Mercury. And now NASA considers to follow ESA's JUICE mission to Jupiter's moons.
NASA and ESA both have fairly diversified mission portfolios. But taken together, they seem to overlap a lot. JAXA's asteroid and comet missions, however, I think can fit with those of NASA and ESA because of the variety of the targets and big differences in mission profiles (Hayabusa, Dawn, Rosetta). And Russia at least aims for the moons of Mars, rather than yet another Mars orbiter or rover.