I don't think the space conquest spirit was ever lost. It seems to me that science-fiction is still largely dominated by space tales. To the extent that enthusiasm has declined, it is largely a product of the stagnation in the technology. There is only so much you can do with chemical rocket engines, and anything beyond LEO (or, at best, the moon) is going to be massively expensive with little real-world payoff. The technology that could take us beyond the moon and inspire people to believe in space travel again would require nuclear engines, which are limited by a strong taboo and international and national regulations against fission devices in orbit.