[shalmanese]

I've found the opposite. When users feel like a lot of work has gone into something, they'll restrict their critiques to minor elements that seem easy to change because they are worried about causing you too much rework. Putting it in a sketch format makes it seem like it was easy to generate and gives them much more freedom to make more radical suggestions.

The key though is you also have to present them at least 2 - 3 very radically different versions of the same thing.

Each tool has a different purpose at different parts of the design stage. When I'm in blue sky ideation phase, I don't want users to be thinking about colors and proximity (although I do, even at that stage, care deeply about information hierarchy and hate sketch tools that make information heirarchy hard to design for). It's when I'm more in the narrowing down stage that I'll move to more higher fidelity tools.