I really see no reason to switch. I've used vi for a long time and am quite comfortable with it; about every six months I would install emacs to give it a go, then quickly just switch back. Yes there were things I much preferred about vi, but the main reason I never stuck with it is because the time investment to fully learn another editor when I already know an extremely capable one isn't worth it.
I'm reminded of this rather dated study.
In my opinion, SLIME is about the only reason to switch to emacs if you're already proficient with vi.
