I am also diversfying from the NW/CO/DL axis of evil, and am switching to *A.
E+ is just that (a plus), but what did it for me is the LH program. Awesome mileage bonuses for J&F, two years of Senator (* Gold) status, and a top-notch route network.
I'll keep flying NW/CO domestically, because they seem willing to fly me in first on a $200 ticket, but I understand that that won't last forever.