The topic of knowledge bases has always been rather interesting to me. I don't think any sort of formal experiment or survey has ever taken place in regards to fighting games, so all I have to go on is my own personal experiences with gaming in general.
First, I'd like to say that for me personally; a knowledge base can be both incredibly useful or incredibly obsolete, depending on the game. I always enjoy contributing to knowledge bases when I can (if that wasn't obvious), but I have to be honest; sometimes I'm really bias or partial for various reasons.
Personally, I believe that learning the game by yourself can be half the fun of a game in the first place. Normally I enjoy picking apart a game on a very technical level. On the other hand, there are some games where I know I wouldn't have made progress at all and eventually would have quit playing without the presence of some form of knowledge base. Some games can be significantly more fun when shared information enlightens you to the possibilities and potential within the game, but I think the opposite can be true for other games. I assume it's pretty much the same for everyone. The intuitiveness of a game and the interest level per each user will presumably determine the need for a knowledge base, in theory.
That said, I also think it's interesting that there are so many different kinds of knowledge bases and how each one can influence another quite dramatically.
There's individual pools of knowledge that circulate within the community around arcades or other meeting places, instant messaging, IRC, FAQ sites, web forums, videos sites, wiki sites, and specialization sites.
With individual arcades the knowledge rarely ever circulates outside of just those people who are involved. Word of mouth can indeed travel, but there's a limit to it. An extreme example of this would be to examine how Japan learned the usage for V-ism in SFA3, and America was left so far behind. Back then, no one really knew the potential of V-ism in the US because everyone was so focused on A-ism and X-ism, and it wasn't until Japan visited the states that we learned just how much better V-ism actually was.
However, you could say that without other available knowledge bases the same thing can occur on a smaller scale, and is probably very common. On the other hand, you could say that with the existence of other knowledge bases they begin to influence each other, often in both positive and negative ways.
A great example of this is IRC and private chats. Just like with offline knowledge, information gets shared and passed through word of mouth within the direct community. But, a lot of things get lost because not everyone can be around 24/7. Lord knows if I log off IRC to go to bed on the day of a new game's release I might miss a whole fuckton of information, because everyone is talking about the game on that very day. People also don't like repeating themselves, players with the knowledge might get sick of saying the same thing over and over, and stop repeating it entirely.
Wiki sites may get neglected by users who actively use IRC and web forums. When knew knowledge is discovered it's passed around IRC and discussed, but eventually people get tired of "old news" and the knowledge is kept there, the information doesn't make it's way onto forums or wiki's or FAQs because they are already tired of it. Even when it makes it's way onto forums, there's a chance that it could stagnate there, being lost in a sea of other posts. Sometimes no one is really willing to go through it all to collect and transcribe it. I've been guilty of this many times in the past myself, where after having learned something new and discussed it, I became disinterested in it and never posted about it or felt like transcribing it after the hype died.
There's also misinformation, speculation, and theory.
Video sites tend to influence other knowledge bases quite a lot, because video data can be interpreted and misinterpreted in many different ways. Maybe a combo wasn't actually valid, maybe the player did a misinput, maybe the player didn't know they had a better option available, maybe "this"/maybe "that" and so on. Certainly, it's also extremely rare that a video tutorial would ever get updated after it's initial premiere, so old footage may become outdated. We also tend to rely on individual analysis of match footage, it's rare that the community discusses every aspect of what happens during a spectated match and why. Discussion threads regarding matches are generally a bunch of people praising the players and critiquing it based on how entertaining it was.
FAQs are also often not updated years after their initial publication, even if new knowledge has been discovered and the gameplay has been reinvented as we know it. Many people simply leave it as-is, and others don't bother writing their own update versions because only marginal amounts of information has changed while the core has not.
Web forums tend to have new posts to correct old outdated information, but old posts tend to linger and never get corrected, sometimes even without any correct followup posts. Or worse, there are those who adamantly defend incorrect, situational, or subjective information based on limited experience, even when the community is disagreeing.
It's also been my experience that a lot of the top players are unable to verbalize what it is they do and how they do it. Sometimes there's also heavy disagreements on technical information between top players as well.
Knowing all this, it's easy to see how incorrect or incomplete information can be passed off on various mediums and never really thoroughly examined, and how there can be a lack of information on a game.
That's not to say there aren't good resources out there. Certainly, there are. But it's extremely rare that you could find an absolutely complete and comprehensive one.
Honestly, I can't really think of a solution though. At least, not a practical one that is even remotely likely to happen in the near future.