There is definitely a sense in which some GMs could benefit from using skill challenges in thier preparation--and then throwing the skill challenge away while keeping the material in it.
I mentioned already that sometimes for me a skill challenge is just a convenient way to record my notes (and it is a lot less work than writing it out in pure text, sometimes). Those notes may or may not inform a skill challenge at the table. It could just as easily turn into an interesting scene with a skill check or three.
But there is also the sense in which skill challenges are a check list, regardless of how you record the prep material. Do you have interesting and fun things that can happen on failure? Does failure matter? What does a partial success mean? Will this interest most or all of the players at the table? Are there things that their characters can do, if they are so inclined?
To the extent that you've already internalized these questions in your prep, and your players are proactively making things happen, then this aspect of skill challenges isn't helping you much. If you've got that player that will always find a way to make Streetwise matter every game--even on an overland trek, then you don't even worry about it anymore. For you, a skill challenge is merely a structure to the action, and will only be useful if you want/need that structure or are driving towards a particular style that benefits from it.
In my case, I've got some players that aren't that proactive (though not completely reactive), and also having a large group makes it hard to juggle. Even though I know all the questions I want to check, it is still easy to miss something useful. Working on a skill challenge during prep, for me, is a conscious statement that this scene matters as a scene that drives the action and takes a certain amount of time (aka pacing). Might not turn out that way, but that is what my initial plan says. Contrawise, if I start putting together such a scene, and I'm struggling, this tells me that at least one of two things is true:
1. The scene just isn't worth a skill challenge, and I'm trying to force it. Rethink my priorities and pacing goals.
2. The scene is worth a skill challenge, but my material going into it sucks. Broaden, deepen, expand that material to make it rich enough to deserve a scene.
I roomed with a guy in college that did all of the above naturally, often winging it. But he was a communication/theatre major and worked as a DJ on a call-in radio show. He lived and breathed this stuff.
