If i was in their shoes and i am not, i would prioritize quest bugs first, because if they come up with a DLC that ties in more stuff together then if the base is broken, the add on will not work.
The quest bugs have been documented to death and they know what they are. They have to sit down and figure the scripting out. I am not a programmer but i think it would be easier and faster to fix a script than trying to implement a whole new set of feature into the game not even knowing if it is not going to break something else in the game.
Bethesda is not the only company in this boat, I have seen many companies dishing out games and leaving them incomplete, but most of them are out of business or out of favor to their fans. It is said by many that the game should be appreciated as a whole and not be examined in details , well i strongly disagree with that. If one was to live one's life just for the big picture and not its moment, pretty much everyone would have no clue who we are or we we are here for. Beth has an oportunity to make a great game even greater and make special moments in the game what they were truly meant to be.
All they have done so far is dance on one feet or the other trying to adjust to the dance of complaints or even outdo the modding community by implementing a new feature like the kill cam. I say fix what has been broken with patch 1.5 and forget about adding new features for now. Clean the errors in the game and polish it.
Then DLC the thing to death.... i ll give you my support and my money then...