I wasn't disagreeing with you, but so far as i can see, nearly all of the benefits you listed are marketing ones, which twitter is practically essential for these days.

In terms of marketing a product, indexation and discovery aren't critical issues, even if it's nice SEO to be able to control it in such a fashion, but i can't see evidence of ranking being affected by tweets.

Thanks for the info re .edu and mention-values, makes total sense.