This advice will get you a mile ... backwards.
Yea, either that or it will get you into your top choice, with interviews at most other top 20 schools you apply to🙄........
The interest in GPA, classes, etc. for med schools boils down to two questions:
(1) Can you handle tough educational experiences and hard science?
(2) Are you better qualified in that regard than the next applicant?
The upper level courses will approximate the rigor of med school classes better than the 100 and 200 level classes. Willingness to take on those classes and ability to succeed in those classes answers the two questions above better than 100 and 200 level classes.
IMO...there are two ways for the average premed/md applicant to go about getting accepted into a school:
1) Understanding that this process is largely about jumping hoops and showing interest in things that a)might not truly interest you and b)might not have a whole hell of a lot to do with the actual realities of being a physician. Succeeding is about understanding exactly how you will be evaluated relative to other applicants and positively emphasizing the aspects of your app that will matter most (namely..your bpcm and your mcat score).
2) the wrong way.
Am I advocating that you should always take the path of least resistance and thus avoid classes that are interesting yet challenging all in an effort to protect that gpa? Absolutely not (even though I admit it may come off as such). All I am pointing out is that if a single class will burden you with an overwhleming amount of work to the extent that it negatively impacts your ....a)performance in other classes...b)time to study for the mcat....c)time to do other meaningful stuff (ec's)....then it is not worth IMO.
For every person I know that threw caution to the wind and did watever they chose and still had a successful admission cycle, I know twice the amount of people who bit off a little more than they could chew either in their course or concentration selection and are now sloging threw a postbacc or smp because in the eyes of many adcoms a 3.3 in physics is not as good as a 3.8 in sociology.
To put this situation into a little more context...the OP asked if a single upper level course would enhance their app. With all due respect to the OP, this kind of question doesnt ring of a great amount of understanding about the app process. As such, I gave a pretty vague and general response that I thought would serve the best interests of the OP.
I understand completely those who would be quick to flame my outlook on being a pre-med, etc....but I say what I say because I think it is just the plain truth and I encourage the OP to take it with a grain of salt. With that said, anyone coming out and definitively saying...."Yes taking harder courses will have a huge impact!!!" is full of it. I respect your thought process for saying this, but the fact of the matter is, whether you are a premed, med student, resident, attendent, or on ONE school's adcom, your opinion is worth just as much as mine.