I disagree entirely with the degree being useless. Lots of positions in the clinical research field, for example, require a science degree. So there's a huge additional benefit to the SMP if you were a history major or something; you can do the SMP, get the science degree, and make yourself eligible for all sorts of positions you weren't eligible for before. If anything, it makes yourself more marketable than a traditional master's during a job interview because you can say that you took so many med school courses, thus making your training that much more relevant depending on the field.
Now, if you already have a BA/BS in the sciences, there's not as much benefit. You may be eligible for a pay increase in you current/former field, but that's about it.