What's 421? I know that 330 was a great class, and that's how I met Kristy, then through her went to TLE and met you guys. So I highly recommend 330 for that alone, but if Linda is still teaching it, drop it immediately. I ended up getting a C out of it--because she didn't give us a syllabus until the last week of class. I had no idea what her expectations were. Occasionally she mentioned that we ought to be reading something or other, but since I had no syllabus to refer to, I often forgot it in the face of other classes which did have the requirements spelled out.
I considered an editing minor, but it would have added time I didn't want to spend. So I took 330, and Mel Thorne's internship, and worked for Mel for just over a semester. My editing classes never come up in interviews, and at this point I'm considering dropping some of my older jobs off the resume, as it's starting to get crowded with what are now minor things (typesetter back in '96, that kind of thing).
The best thing I can tell you is if you have a choice between an internship and a class, take the internship. Between a job and an internship, take the job (related to publishing, I mean). The more hands-on real work you get, that's what matters. And nobody cares if you weren't an English major or an editing minor--in fact, it's stronger sometimes, depending on what you want to do, to have a degree in something else, as long as you have the job experience.
For example, here at my job, in the school division, they tend to want editors with elementary teaching experience, since they're working on school textbooks.
If you're going to get burned out, cut the fat and finish to get that little piece of paper that means so much to everyone. Keep an extra editing class if you have the time, but don't worry about the minor.