I agree that a DJ should talk - good ones can create an atmosphere.
A good DJ in my opinion is someone who is excited about the tunes he's playing - I think a good example is Mr Barnfather. He's always excited about the stuff he plays - and that's infectious, it spreads to the dance floor. Richard S was another good example.
This applies not only to DJing - but to other work as well. Particularly marketing and selling - how can a punter get excited about your product if you're not excited about it.
Having said all this I don't like mumblers who you can't understand.