Here's an interesting tidbit I picked up from Rebecca E. at the Derbyshire Writers' Guild:

Gracechurch Street at the time was known for some radicalism . . . While I think that Austen was telling us something important about the Gardiners by telling us their street address, I don't mean to imply that she'd have them be too outrageous in their politics. They might want reforms, but not revolution. As an aside, Mrs. Gardiner's comment on Darcy ("His understanding and opinions all please me." P&P; Chapter LII) has always suggested to me that Darcy is more liberal-minded then we might be inclined to think he would be as a man of such privilege.