I think what makes her storyline dull is that she's portrayed as this irresistible force totally immune from the political and military quagmire plaguing all the other major players on the show. There has been no recent twist, no intriguing subplot related to her story. Coupled with the fact that everyone is well aware of her ultimate goal and she's drawing towards it at a snail's pace despite having the means to finally fulfill it makes her arc incredibly frustrating.
The only obvious twist remaining in Dany's story that I can see is her finding out that Jorah was an informant and betrayed her for a time, before switching his loyalties.
They touched on this last season in episode 5 when Jorah was trying to deduce whether Barristan knew of Jorah's deceit, they ramped up the tension between them for awhile and it hasn't been mentioned since.