I wore Sidi road shoes for years and had horrible hot spots with my Speedplay X-2 pedals/cleats. I recently switched to Shimano shoes, for both road and mountain. What a difference. The biggest factor was the wider toe box. I also moved my cleats back from the neutral position.
I don't find it any harder to unclip from my road pedals (X-2s) than spds or Frogs. If the walking bit is your concern, than keep your mountain shoes/cleats.