Yeah, it's been done, and there's never been any question that dry ferts are *far* cheaper than wet ferts. ...Though I'm not sure how many do the math.
Right now, however, with the big to-do about possible toxicity in one or more of the micros (possible, given a fairly specific set of paramaters, but that's enough to make people start thinking, and worrying), people are looking for other ratios. And since only a handful of the many micros in CSM+B are available, individually, at reasonable prices, in useful chemical forms, there's a renewed interest in wet ferts ...micros, at least. People are scrounging for the right combination that will allow them to cover the expensive elements with a premix, while being able to add the cheap elements in other, preferably dry, forms, without overdosing the potential problem elements.
So, with dry ferts, it's a no-brainer (mix your own, you lazy bums
). But with micros, it's a little more of a gray area. Which is unfortunate, since the micro mixes are pretty expensive.