I've always run 45 PSI and haven't had any unusual wear in the middle and can still take the exit ramps at 60. I'm thinking of getting either the Insight or Civic Hybrid tires when the current ones wear out (which is soon, and snow is on its way) - but I'm sure handling will suffer :-(
Reducing the diameter but also, based on racing principles, the lighter the weight of the rim has a huge impact on not only the handling, but in fuel economy (The "Unsprung Weight" Principle). It takes less energy to get them going and less to stop (like a flywheel). Unfortunately, lightweight rims tend to come in larger sizes (unless you source them from a hybrid).