My initial mental reaction to this was that there's not necessarily going to be one absolutely correct way of completing any particular mission. It seems at least partially true that if you solved the mission, the exact way in which you arrived at the solution shouldn't matter. You also have the opportunity afterward to review the forums to get a feel for how others might have approached the mission or what kinds of problems they ran into.
It occurs to me ofc that some people might just solve the missions by following walk-thrus or w/e. They end up solving the mission, but they may not learn as much in the process. It's not the way I would do things, but I guess they only rob themselves of the learning experience.
I do think if you want to get the most out of the missions, there are some basic guidelines you can try to adhere to:
(1) Always begin by trying to solve the mission without using any external resources.
(3) IIRC, there isn't a single Basic Mission where you should need to resort to the use of any 3rd party tool. So although you could for example solve some missions through brute force, it hasn't been my experience that this is necessary and you obv won't learn as much if that's your first solution to every cracking problem. Once you start working on the Realistic Missions, I think you sometimes have to resort to the use of tools, esp. as you don't necessarily want to reinvent the wheel when it comes to stuff like decrypting hashed passwords, etc. Even then, my goal is still to get as far as I can and understand as much as possible about the problem first, only looking for appropriate tools when I feel I've exhausted other ways of approaching the problem.
(4) If I get stuck, I go to the Mission forums. Although sometimes the suggestions come pretty close to being spoilers, I generally find they push you in the right direction without giving away the answer. I do think starting with the forums is likely a mistake though -- I've learned as much if not more when I was approaching a mission from the wrong angle.
(5) If you do end up stumbling upon a spoiler while doing your Web searches or w/e, take the time afterward to understand why the suggested solution works. This has only happened to me once so far, but I learned a lot after the fact by studying the code I found and thinking about how the author would have arrived at that approach to the problem.
After thinking about it some, though, I don't really hate the idea of having an official solution that gets unlocked when you complete the mission. If you did solve the problem a different way, then the solution might teach you something new and sometimes there are parts of it that you got through but you wonder if there would have been a better way to attack the problem. There's at least a couple spots I got through by trial-and-error and I remember wondering if there was maybe a more elegant way to have approached things.
Personally, I wouldn't mind seeing some alternate forum themes.