I tell you what, they are dangerous!
Well, I did own a comic-book store for 10 years. So...the reason for capes was just to show some action in the panel. Japanese manga nowadays just puts in speed lines (Not to be confused with lines of coke!)
The reason for the leotards was because they were trying to copy the circus muscleman look of the day.
I really can't explain the underwear worn over the leotard look though. Still baffled by that one.
I should go watch The Incredibles. That was a great movie! Funny thing about that movie. The first Fantastic Four movie was delayed because when The Incredibles came out, when Elasti-girl stretched it was soooo much better than what the had planned for Mr. Fantastic. So the studio had to go and change all the special effects because some characters that were based on the FF were done better than the FF.