And here's the question: do you think that DM's today need more "hand-holding" than they did twenty years ago? There seems to be a need to have every eventuality mapped out in advance, keeping the players on track, rather than running with it and seeing where everyone ends up. Is that where you see the adventure designer heading, or is there still room for a more "Gygaxian" approach to adventure design?
Meomwt, it's a great question without a single answer, because different players and different gamemasters need different things. I think that a Starter Set or Beginner Box that doesn't do a lot of handholding is failing in its primary goal, which is making it easy to learn the game. I wish that the blue box had done a bit more handholding back when; it took me a while to figure out how basic things were meant to work.
And there's room out there for railroad-like (or adventure path-like) adventures, that are meant to keep players on track. I've played too many aimlessly wandering and incoherent scenarios where the game is "what do we do next?" because there's no clues, track, or goals stated in the early going, the middle, or toward the end. Most players like the occasional sign, and the more convoluted the plot and premise, the more handholding is appropriate.
But in the end, I think a lot of the joy that people take in great sandbox adventures (like, oh, the Lost City by Zeb Cook, or the Kingmaker adventure path) is the joy of making their own way and *uncovering* the goals and being the active, heroic figures who decide what to do about something. Done well, this sort of scenario is less about handholding and more about enabling discovery and presenting wonders at every turn.
And finally, there's the category of adventures that really are about piling up dangers, conflicts, and NPCs with opposite aims, and letting someone light a match. There's just no good way to plan out every element of a rogue's guild gang war with any certainty. There's chaos everywhere. A very fine scenario can be made out of a list of NPCs and their goals and resources; think of LARP play.
So where does that leave adventure design? Yes, I think there's room for scripted, guided play, especially for newer or less confident players, those who want maximum help. And there's room for adventures that provide inspiration, some great NPCs and dramatic scenery, and trust that the players and the DM will run with the parts that entertain them, spinning out their own story.
RPGs have always included an element of performance (watch me play my character as a badass! watch me give a cool villain's monologue!). They have also included elements of improv because they MUST rely on a DM at times (your character does WHAT? Well, ok, here's what happens...)
In other words, there's no one size fits all, and I hope that more experienced players show their skill at play by making adventures their own. A poor player can, of course, complain that any given adventure doesn't answer all questions. But many of the most memorable moments, for me, come from when a player puts a bit of their own magic into the game, because he or she knows what the party likes, what his friends like, and how to make the game awesome. That's always going to be a function of play, and good design leaves room for that. A tightly-scripted or detail-crowded design tries to cover everything, and fails to leave room for what I would consider more interesting and spontaneous play.
That's my take on it: design styles need to serve particular play styles or levels of experience, and no one design style is going to please everyone.