Planning nondegree classes
The reputation of the faculty member helps somewhat, but is nowhere near as useful as the quality of the recommendation letter. A letter from a famous person who doesn't really know you outside of the classroom (or doesn't know you at all) isn't nearly as helpful as an in-depth evaluation from someone you know well, and who knows you well.

However, I find the notion that you would taking an introductory course versus an advanced elective somewhat concerning. In general, if you are looking to buttress a graduate-school application, evidence that you can handle graduate-level work in the field matters far more than having a Big Name write you a weak letter.