Much of the blame for vapid content propogation on YouTube must also be assigned to YouTube's own content recommendations engine. This:

Won't accept no for an answer. You can't select and item and say "never, ever, under any circumstances, show this to me again." You can't even delete it from the recommendations list.

Once you fall down a YouTube rathole, you stay there. YouTube never forgets (or requires a severe amount of ass-kicking and browser/history deletion to be told to forget). Random crap content I've viewed long ago seems (and of course, I can't know for sure) to result in promoting the same sort of crap content. You've all ended up in that corner of YouTube, and there's no way out.

YouTube promotes its own recommendations over what you've searched for. When I look for content, rather than have the search results represented in the recommendations list, it's YouTube's own selections. Which are often ... not what I want. But don't be tempted to click (see "rathole" above).

Mass markets favor common denominators. There's amazingly good stuff on YouTube, for whatever your definition of amazing is. But often, that's going to be ver specific to who you are and what your interests are. The only thing I can guarantee is that the intersection of your interests with the rest of the world is likely to be at a pretty base level.

Eyeball economies favor vapidity. We're seeing this in many areas (news, Web content, videos). Until user-selection tools become better at countering this, we'll continue to see the problem.

There is really good content with relatively poor production values. Having an interest in fitness, Boris "johnny mnemonic" Bachmann's "Squat Rx" video series is _great_. It's a one-man production filmed at low (320p) resolution with spotty audio levels. But the depth of knowledge is excellent. Thankfully, it's filmed with a tripod and well edited. http://www.youtube.com/user/johnnymnemonic2

Production quality doesn't translate to high-value content. "Vsauce" is a highly-produced video series. The information content is virtually nil (and the energy level is beyond annoying). The "origional series" "Blue" is ... beyond stupid.

Production quality CAN further boost high-value content. The TED Talk video series, and RSA Animate videos are excellent. If viewed from a production perspective, there's a lot of work that goes into them, and poor imitations are poor, though some other parties have used similar techniques well, see the Post Carbon Institute: http://www.youtube.com/watch?v=cJ-J91SwP8w

YouTube handles spam / MVP poorly. A popular video will be grabbed and repurposed by spammers and mindless video propogators / mindless viral propogators endlessly. It results in a huge duplication of content (often at increasing levels of video/audio quality degredation). See especially "fail" video compilations. No, it's a trap! (See: "rathole", above).

Chalk it up to my own boring interests, but finding micro-channel content relevant to specific areas is one of the huge wins of YouTube. Interviews, seminars, conference sessions recorded, and other informational content. Along with a bit of entertainment. The problem of course is that such content has very little visibility at scale -- it's part of the "long tail". And despite what some Cluetrainists would want you to believe, the real money is still at the head.