What concerned me about Emily's post was that she didn't mention whether or not the devs knew for a fact that only a fraction would play the game on whichever setting had less content.
Of all of your suggestions, though, I liked your first one the best. They had this in the first STS. (I don't know if it was in any of the following). It meant that pixel hunting wasn't needed at all.
I kind of like the last one, too, but I think it's one that would have to go into a "difficulty" setting. Sometimes half the fun of the game is in combining objects. (Not on TMI, though. Putting an object onto either plate before combining looking good in the video but was far too time consuming in the long run). On the other hand, if it was possible for the protagonist to tell you if an item in you inventory needed to be combined with another item, in your inventory or not, when you click on it (on a certain setting)...
If we're talking about a difficulty level that can be adjusted at any point throughout, like an extension of the current hint systems, then it might be nice if the indicator was more descriptive in what that level does. IE, setting one will tell you that it will drop a hint every [X] minutes. Setting 2 will tell you this and will tell you another thing it's going to do to make it easier (eg; highlight items you may interact with). Setting 10... Well, if you're adding this many things to make it easier I imagine the game will be playing itself for you to watch, much like
this. (This was posted on the Adventure Gamers thread).
I didn't post this on that other thread but I thought an "easy mode" wouldn't necessarily need to cut out puzzles but maybe the computer can do some of them for you to speed things up.