I think space has already been sold to the public. I notice that space related stories on BBC news are always high ranked in the most read column. Like today, Elon Musk's comments about Ariane V are second only to the ongoing Gaza bombardment.
I think the interest is there, the enthusiasm is whats missing. And if you want to build enthusiasm about space exploration my suggestion is give people something to be enthusiastic about. Only so much excitement can be generated over Curiosity taking photos of yet another red rock.