Depends on the flaw and how its used. Cable TV in particular sure is in love with flawed characters so they've become symbolic of "better" drama.
Kirk being cocky wasn't a signal flaw for him because it never seemed to cause him inordinant problems. His signal flaw, if he had one, was being overly dedicated to Starfleet, to the exception of his personal life. That theme popped up every so often as a source of angst for him.
But Kirk was not so much the standard flawed individual so much as a fascinatingly complicated person. Anyone who could be both too cocky and too serious has got a lot going on. Ditto for his girl-in-every-port attitude contrasted with his apparently sincere caring for his crew...that's not an emotionally shallow person there.
Spock was more of the flawed-type with the single, signal flaw, and that was also used to good effect. I see a lot more Spock types of characters vs Kirks in fiction. Probably easier to focus on the signal flaw of a Spock type when writing him vs trying to corrall all the complexity of a Kirk.
The one thing you don't want in a character (unless its a comedy) is a flaw that elicits contempt from the audience. A character can be a strutting egomaniac like Dukat and still have fans because he's not a weakling.
I'll have to drag in poor Anakin Skywalker one more time for a counter-example: he was also a psycho, but the wrong kind, a weakling - stupid and overly dependent on the emotional support of others. All Lucas had to do was write the guy like Dukat and cast an actor to suit, and maybe it still wouldn't have worked but it wouldn't have flopped quite so badly.