The algebra study is worth it for a STEM field. It cost about the same as the AP exams which USAFA doesn't give credit for either but other schools will. It counts for some majors. I don't know OPs major. But if OP is considering dual enrollment for College Algebra and is strong in math, a CLEP would be a lot easier than the time and money of a dual enroll with the same benefit of college credit. Just an idea.
I agree that algebra skills are imperative for STEM fields. My recommendation would be that OP keep those skills sharp on his own time with free resources. They should take AP Calc (and take the AP test) and AP Stats. CLEP or DE algebra is overkill.
Now for some comments about AP exams, validation, CLEP tests, and DE credits:
USAFA doesn't give
credit for AP exams, but they do use AP exams as validation criteria for certain courses. Most majors at USAFA are "overloaded" in the sense that the total required number of credit hours for the major is over the minimum required number of credit hours to graduate. If a course is
validated (not transferred), e.g. Calc I validated (in part) by the AP Calc AB test, then the total required number of credit hours for any USAFA major is decreased because Calc I is a part of USAFA's core curriculum. So while an AP exam doesn't transfer credit, it can still reduce the total credit hours that a cadet will take at USAFA and therefore make their life easier. Of course, validating courses only makes sense from a credit perspective up until the point where a cadet needs to take additional courses to meet the minimum required number of credit hours to graduate. Even then, those extra courses can be pretty much anything that is of personal interest.
USAFA does not accept DE courses if the course is counted towards fulfilling high school graduation requirements, i.e. on the high school transcript. It will look good on an a USAFA applicant's academic profile, though probably won't be the deciding factor in gaining an appointment. In general, dual enrollment courses only transfer to other colleges on a case-by-case basis according to the specific college's policy.
USAFA does not accept CLEP tests. A fair amount of universities do not accept CLEP tests, including many "premier" universities. If OP is competitive for USAFA, then it is likely that they will also be applying to other "premier" universities.
Whether DE or CLEP, college algebra credit is not going to go very far, if anywhere, towards fulfilling STEM degree requirements. Most STEM degrees start at Calc I. It might count towards fulfilling a math requirement of a fuzzy liberal arts major, provided the college accepts the DE or CLEP credits.