You brought up some really good points. Your second point about interest--that's a great point. I think interest--and, subsequently, focus and attention--are force multipliers, especially in a field like programming, where experience and expertise don't just help you lay more bricks, but actually increase how many bricks you can lay in the same unit of time as before.

The negative effect is interesting. I've heard it said before that non-experts often come up with novel solutions in some fields. That might because of what you pointed out, that the experts are too focused on a certain range of solutions, so they might be missing out on a range that a "layman" can easily identify.