If you want to get moved to E+, you can always pay for it (annual fee or individual flight fee). There's always a chance that E- will fill up so one strategy is to not get seat assignments until check-in in hopes of getting an E+ seat. The risk, obviously, is that you might get stuck in a middle E- seat.

It's too bad your N/S flight was cancelled, but that's always a risk flyers take. Seems as though the airlines have offered the best other flights they can give you under your time constraints.