While this is likely true for designs, I believe there's more to it. I switched from straight to cartoon lines for my architecture / planning diagrams and suddenly started getting more unprompted comments about how they're clear and approachable.
Personally I also prefer the hand-drawn style, but can't put my finger on why. There's something about the uneven lines filling out the space better, while still defining the shapes well.
I think you're pointing to the positive case of the same effect, which is that people use "hints" from the level of detail of something to determine the level at which they ought to inspect something.
Lower fidelity puts the viewer in a more conceptual mode of assessment, and there they can more easily perceive the clearness/approachability of your concepts.
Personally I also prefer the hand-drawn style, but can't put my finger on why. There's something about the uneven lines filling out the space better, while still defining the shapes well.