On its own youtube doesn't really make any money. It's only recently that its started to actually champion original content. (as in something approaching a tv station. not just nut shots.)
[http://www.quora.com/How-much-money-does-YouTube-make] (granted not the best of sources)
But we need to separate "value" from viable business. Twitter, unless it changes will go bankrupt. Its loosing around $160 million a /Quarter/
Value is a subjective thing, and can be manipulated to suit the needs of others. Earnings are meant to be empiric. If twitter was any other company, its stock would be worthless.
If we take a look at the buisness model of youtube:
o Collect all video
o Flog adverts on those videos
o only take down copyright when notified.
o Sign deals to distribute promo material.
o Force small producers into exclusive deals with google at discount rates.
The signal to noise ration of profit making videos to not is terrible. I suspect that 99% of all videos uploaded to youtube are useless and have less than 100views. (https://www.youtube.com/yt/press/en-GB/statistics.html)
Without the backing of an extremely profitable company such as google, youtube would have failed. I'd assume it would have been sued out of existence, and if it didn't it'd have died under the infrastructure bills (they basically have free bandwidth and CDN)