I applied to 12 schools with a 3.05 cum, 2.97 BCPM, 28O MCAT. 7 Interviews so far, two acceptances (University of Louisville, Howard), 2 waitlists, 3 schools I haven't heard from yet. I received a full scholarship to University of Louisville. It can be done, but you have to have a strategy.
Take a look at my MDapps. You will see what will happen if you try to take upper level classes only to impress admissions committees. I am done with the process (Finally!) and can say that the admissions committee briefly screens the applications before they decide to give you an interview. They are not looking over every class, but rather looking at the overall BCPM and cum GPAs. If they look at individual classes, they look at the individual grades, not so much at the title of the class. So it is to your advantage to take the classes that you can do well in and boost that BCPM GPA. However, I do agree with taking research for credit.
If your goal is to stand out in the admissions process, I suggest identifying an overall theme about YOURSELF, not your grades or academic record. This could be a challenge you've overcame and how it relates to your determination, or the reason why you want to pursue medicine and how that has influenced your path (research, traveling abroad, extracurriculars, etc). You then need to push this agenda every time you can--in the personal statement, the secondaries, the interviews. Everything you write or say needs to tie back to your overall theme.
This is how you get into medical school. Not by taking extra difficult classes for no other reason but to impress committees. Standing out by taking hard classes is based on the assumption of a normally distributed applicant pool--meaning people with Fs, Ds, Cs, Bs, As, taking both challenging and easy classes, and people who have many extracurriculars and none at all applying. This, however, is not the case. Most people applying to medical school have higher GPAs and standardized test scores than other college students, so the applicant pool is highly skewed. You will find that the majority of the applicant pool has taken "hard classes" as well, so in the end you would look average anyway.