Unfortunately i've already been spoiled about the thing you mention in your spoiler warning(and a few other things as well) thanks to all the book-readers who lost their fucking shit all over the internet because the tv-show apparently removed some important book-stuff from the final ep in season 4. >_>
I'm always worried about what they will do when they eventually catch up to the books, and how they will deal with the child actors rapidly out-growing their characters.
Nerver really been too worried about the productions costs tho, since i always thought the insane popularity of this show made it earn back the money it cost to make.
Also, I strongly doubt that the fans/actors would start "dictating the plot" and the studios would cave under the pressure and start making massive changes from the books.