That's kind of the point though - I had no idea this feature existed until they started pushing it to me. I think it's too much to expect users to opt-in to things. How would I have known to opt-in to this? Yet I am now much happier because they improved the UX for me.
I think opt-out makes sense though, for users who don't a feature.
If you put it on a single, easily recognizable, easily accessible page (all new features, etc.), then many users will find it. You can even give a notification when a new feature is added (as long as kept to a reasonable amount).
Features that will go viral are worth adding for all, features that did not can be kept there.
You overestimate what people will understand from a technical description in a configuration option. Even if they were experimentally inclined, which most people are not, they probably wouldn't even notice the effect, particularly if not a new user. Twitter is a black box for most users.
Twitter very likely did market research on its effectiveness for the target market they were trying to please. Probably that's just not you.
But what if most people like it? I have to say I think it makes a lot of sense. If a high number of people I follow like something, you might want to show it to me too.
Bundle it under "experimental" or "advanced features" in an easy to use page with a very clear explanation of what each feature does.