Miyuki was my early favourite in Lucky Star (but only in Lucky Star; she never reached the status of all-time favourite (yes, I am one of those people (and the favourite's identity must remain a secret))). So, naturally, I took a note when she was taken as an example of "smart" [link, link]. Au contrarie, I thought that Miyuki possessed a large store of trivia, but was not generally "smart", unless we define "smart" as "smarter than Konata". Even then it's a big question, because the application of oneself plays such a big role.
As an aside, I wish to note that I reject the notion of "multiply intelligence". That codeword was invented to raise self-esteem of dumb people. No, the value of g and the curve are real. What I do instead is to give Konata the benefit of the doubt. She might have some g, misused and underdeveloped.
Another funny thing Miyuki brought about was a notion that Miyuki is "smart enough to be a doctor". This is unintentionally funny, because the dumb doctor terrorists in Britain this year made lots and lots of people to come out of woodwork with stories of dumb doctors. I do not remember where I saw it, but one guy commented how in his university medical students pulled the dumbest pranks, and also had a rock band called "Perry Stalsis and his Abdo Men" (Google was no help in locating the comment, alas).
With all that said, I think Miyuki could make it as an engineer at least at some level, and Kagami could probably have a nice career going, maybe not at Von Braun or Kelly Johnson level, but somewhere out there. To be the next Burt Rutan, a girl, in addition to being smart, has to be a much bigger asshole than Kagamin. She is still fundamentally too nice.