Her solo is only 5 issues and is pretty fun. She's married but that's not all there is to the character, she has grown exponentially from her early days.
Invisibility is a power that's useful in many situations not just espionage roles. And even then I think that would make the stories boring if that power is only limited to those type of stories. The range of adventures the FF have enbles her to use that power in cool and interesting ways.
You don't enjoy the FF, it is what it is. But to say the character should never be in a leadership role because you personally don't enjoy them is a bit insulting for those that do enjoy her. There are characters I personally don't like but I wouldn't say things like that because they have their fans who deserve to see their faves get some shine.