I don't really agree with the idea that games are/were only fun because of nostalgia either.
One thing I wonder about your game?
Was it really more freewheeling because the rules promoted it, or because the people playing were under the impression that the system promoted it, so were more willing to accept it?
Well, that's why I drew a distinction between old-school rules and old-school social contract.
Although, I think old-school rules more or less necessitate a freewheeling social contract; there's so much stuff that the rules simply do not cover (all the material that in later editions would be handled by the skill system, f'rex). If the DM isn't allowed to fill in the blanks by fiat, there just isn't a game any more.
And it's not like we had long conversations beforehand about the social contract and the rules system. The players were coming to BECMI more or less cold.