I really liked Daniel Tunkelang's summation of excessive Twitter following as the attention economy's equivalent of a Ponzi Scheme.
Being efficient in Twitter is really a study in transactive memory-- figuring out who knows what and making the connections we can depend on to complement our own knowledge. In other words, it's about identifying who knows certain information, not necessarily investing in learning/encoding the information itself. Of course that assumes your goal is using Twitter as a means of information-seeking...
Regardless, a transactive memory system is an interesting framework to understand our interconnections (why we follow and are followed). Dan Wegner is the brilliant psychologist who devoted much of his time in the mid-80's to crack the code on transactive memory -- transforming people's perception of a "group mind" from a term associated with blind herd mentality to one that takes into account the complex gestalt of a group.
Another way of thinking about this is whether the group mind of Twitter is an echo chamber of bandwagoning or a rich social network that, in Wegner's words "transcends [such] uniform agreement."
The question goes back to your motivation for following. Do you depend on communication with the people you follow to gain access to information, or store expertise you lack? For presumed reciprocity in order to broadcast your message further, yield more 'influence'? To validate our own opinions and beliefs? How similar vs. diverse are the individuals that make up our networks?