I got the cape today! I didn't really take too much time last time looking for the cubes before but I went back and most of them were easy. The ones that gave me a hard time were the ones with the invisible platforms. I didn't expect it and it can be easy to miss them. But it was good stuff.
Like any game I play, I doubt I'll put in the effort to get every last thing the first time through. But if some are really well hidden, it makes for greater replay value and more rewarding exploration.
What I would like to see is more awesome sights and scenery that are waiting to be found. This game is beautiful and finding some gorgeous view or location on top of the dots is even better. Judging by what I've seen I don't think I have much to worry about. But it's like other games, maybe instead of an item or something, you find additional story information in the form or logs or whatever, and since this game tells a story more visually, and it's beautiful, seeing really incredible sights off the beaten path would be, well, incredibly enriching for the universe.
That's just my 2 cents. I can't wait for this game.