Re: What Makes An Iconic Superhero Costume?
I believe a unique logo/emblem is very important. The character should have a symbol that means them (or possibly their team), a signature. If their look is going to be iconic, then that's the single most important detail. Best examples: Superman, Flash, Batman, Spider-Man, the FF.
Colors, capes, lines, accessories; these are things that come and go, working for some characters while failing on others. Frex, Pouches are generally a no-no, but Batman's utility belt looks fine with them.
I'll echo some other sentiments: there is elegance in simplicity. Modern designers (and re-designers) need to revisit this most elemental of design concepts. No more than three colors (I'll say usually, though I can't think of a good counter-example) and in good contrast/complementary style. Also, a definite distinction from street clothes; it should be an obvious uniform.