I have been fortunate enough to fly both the A320 and the B757. I have to say that my time on the A320 most definitely buggered my scan. I used to fly the bus with the automatics and f/d's out regularly, but the wonderful big pfd's meant that my scan was becoming non existent. The one area I truly realised I was getting lazy was pitch and power. Now that I'm on the B757 I realise that pitch and power are king. I regularly fly f/d off take offs and landings, which are perfectly safe as I maintain the skill regularly (not just for sim's etc).
When I go back onto the bus (inevitable at some point), I still intend to fly with the automatics out and f/d's off, but now I would also fly without the bird, which would help maintain that sense of pitch and power.