Sure, Coulson's fanboyishlove for Captain America made for some funny bits during the film, but in a metafictional sort of way, it's a mirror for the love and belief of heroes that the audience might share. Just like Coulson being absolutely devoted to Cap, we've all had our moments where we looked up to heroes of our own and believed in them.
Coulson reassuring Thor that Jane Foster is safe, and he's done it in such a way she doesn't know she's in danger. No further words are required: the look the two share is enough.
Even before that, Tony, despite him treating Coulson unfairly is willing to let Coulson use his private jet to visit his girlfriend in Portland.
Coulson knew what he was getting into when he stood up to Loki, but he still did it because he believes in the Avengers completely, enough to sacrifice his life for Thor.
Also, the fact that he uses the BFG that was reverse engineered from the Destroyer, and not one of the Phase 2 weapons really highlights his faith in the Avengers project.