Wow, ok.
Uh, explain if you're asked...! I said IF it comes up in an interview, you'd have to explain why you took it. You can't plead the 5th if you want to actually get that med school seat. And no, 'random courses' aren't necessarily a good thing. They want to see you making good, productive use of your time. If you just say that you were interested in Botany, they might probe deeper. If you're going to take 'random classes' they usually want to see something challenging and upper division. i.e. Genetics, Biochem, Cell Bio, Molecular Bio, Immunology, etc. I'm not saying you shouldn't take a course you're truly interested in, but just be prepared to defend it well--adcoms and interviewers are not stupid.
Reread my original post...I didn't say it might not help IN your case. I said it might not help your case...'your case' referring to your med school app. You want your app to be squeaky clean, the adcoms look for reasons to toss your app in the later or never box. If your science GPA is really high, they will look for reasons why...and if you have some random lower division sciences that are not required it might raise a red flag.
And you said you've got volunteering 'covered'. Just remember that there are always extracurricular ways to improve your app, and often times those make you stand out quite a bit. You're not just trying to make tick marks next to a list of typical premed activities, you should be trying to really make yourself an attractive applicant. You might very well have a lot of quality ECs, I'm just reminding you that there is almost always room for meaningful improvement with this part of anybody's app.
Good luck with Botany, since you've already decided. I just wanted to go ahead and answer the questions you asked of me.