I think it rather depends how one proposes to make a service which relies on user-contributed content anywhere near reliable. ASBs changing human nature is probably one's best bet - and one which would have very wide-ranging consequences. A world in which people no longer have a desire to gain notice through dyssocial acts would result in a completely unrecognisable society.
Without changing human nature, you're going to need to change Wikipedia. Perhaps if Sanger had stayed on-board he could have tried to impose a more organised structure, perhaps with all submissions being approved by verified experts before they appeared to the general public? That would probably have killed a lot of its buzz as a virtual sandpit, though. To my mind Wales took Wikipedia the wrong way by trying to monetise it - once you start slapping ads on every page, academic accuracy and respectability naturally take second place to getting hits. Admittedly, if they'd stuck with a donations model they would have gone under years ago. Maybe one of the big foundations takes it under their wing?
Kabraloth - I think you're underestimating the effect a successful mass-participation academic project would have on the Internet as we know it. Thus far the Web has generally been viewed as a bit of a joke by the traditional press, because the 'rabble effect' tends to degrade any attempt to challenge organised media using free contributed labour.
Interestingly, one of the consequences of a successful Wikipedia could be less personal sites and weblogs - a factually reliable, communally-edited online encyclopedia would erode much of the need for a personal soapbox. There are always going to be those who claim their opinions are excluded by majority rule, of course, but it's going to be harder to claim sinister government suppression. Perhaps the conspiracy theory 'bubble' of the early 00s is butterflied away?
The flipside, of course, could be more censure of the Internet by individual governments. Only a few governments OTL have bothered with Internet censorship because it's primarily viewed as a communications medium: sure, there are lots of opinions, but reading outside your immediate society it's hard to get a clear picture whether you're reading universally-recognised truth or a lone nutter. A successful community-driven worldview would be something entirely different - if Wikipedia got even half as much traffic as it did at the height of the hype it's going to command a sizeable international audience, with an ethos that makes it extremely hard to control. Would it even be legally possible to stop government secrets being leaked? At the very least I see most governments trying to block their citizens from contributing.