For both options below, first and foremost the Math Department should be institutionally
In my book this means letting students try to do what they want. Err on the side of bending policy to help students with unusual paths. Don't make students retake things they've already taken if at all possible. But, do give warnings if your institution has above average content in the course in question, this sort of advice requires some individualized care and attention to detail. On a personal note, this is one of the things which pushed me away from engineering and towards math and physics as an undergraduate. Both the math and physics departments had faculty who cared to advise me personally and I never felt appreciated or challenged in a positive fashion.
A possible high road to growing the major: (here I echo the excellent suggestions of the OP)
- Share scholarship in general education courses. Don't succumb to teaching the course from the book. Instead, spend a summer to read old books, brush up on the history and write your own notes with which to teach the course. Also, write your own homework which is shockingly dissimilar from the math your general audience has seen throughout previous course work. Prove things like it matters. If you do this right you can attract elite students from majors outside math who thirst for analysis which is not surface level. Once upon a time, I taught such a course and it helped me earn us a new math major who went on to do significant work in graduate school and beyond.
- Generally, try to make the major as serious as possible. Build two or three semester sequences which dive deeper into core subjects. The goal here is not to weed out students, the goal is to teach students a broad and reasonably mature picture of math which sets them up for success in their future endeavors.
Downside, you will scare some students in the above approach. Certainly the weaker students need individualized reassurance in the midst of the above style. But, if you have a relatively small class size with a few good students then it can work. Also, if you have no students who endorse the program of excellence then it creates an unfortunate dynamic where excellence on the part of faculty is perceived as unreasonable behavior by the students. When the philosophy of the faculty and students are unaligned there is real danger for damaged morale for all parties. Upside, the new students you add the major will be sincere in their focus on math since sincere mathematics is what drew them in to begin.
A possible low road to growing the major:
- maximize the number of electives in the Degree Completion Plan (DCP)
- minimize the difficulty in required courses in the DCP
- maximize the choices of math electives so students can avoid subdisciplines they don't care for. For example, provide a path around too much probabilty or statistics. Or, provide a path around applied math for pure folks. Or provide a path around pure math for applied folks etc... general idea: don't make people do things they don't want to do.
- don't require physics or computer science, allow many courses to fill these slots in the DCP.
In summary, make the major as easy as possible. Upside to this approach: you will get more students. Also, with so much flexibility in scheduling, there is a good chance the students taking a given course actually want to be there. Downside, these new "math" majors may not really want to take all your math classes. Also, you will need to warn students that your "major" doesn't really prepare them for graduate math. Also, the lack of computer science and general lack of well-rounding in physics, chemistry etc. may give some employers pause on the applied side.
Probably the low road better describes the position we are pushed towards when there is fear of downsizing and such. The high road is not easily maintained.