2 things that are in great need.
1. Competition
2. Great, charismatic wrestlers.
Listen... right now. Mainstream wrestling storylines in the US... most of them have always been stupid or look like they would suck if you read about them. There might be one, or even two occasions a year when something great would come together, and produce a good storyline. Even during the Attitude era... there was some really stupid shit. Austin and The Rock were just so great, that they could overcome this, and make it seem worthy with their amount of charisma. Mankind and The Undertaker to a lesser extent did this as well.
They're also things like overexposure, and cynical fans... but those things can seem like nothing when you have those two things. Competition's a problem though... as the only thing that could help TNA at this point, would be someone like Ted Turner buying them... that's TNA's only hope of getting into the mainstream.