If someone's already using certain things frequently, they clearly know how to get to them; I'd personally be very irritated if the UI started changing to "fit

If someone's already using certain things frequently, they clearly know how to get to them; I'd personally be very irritated if the UI started changing to "fit my needs", which are already taken care of by the UI. Culling features out, however, is not a bad idea, but one has to wonder why you wouldn't focus on making the features easier to use and more useful, rather than dynamically culling them away.