Robots make for great expedition R&D. They can gather a lot of information very cheaply compared to manned spaceflight.

I'm not sure space travel has to be profitable. Certainly Christopher Columbus's voyage was not considered (by most people at the time) to be profitable. Yet economies of scale could definitely be taken into account. It is often said that the computing power of the Apollo missions to the moon were less than that of a TI calculator. It seems we should be able to have unmanned missions to the moon by private sector or even partially public funded. After all were sending DIY cameras into near space.