I think the MD90 crews would be LUCKY to fly the E170 so long as the salary was not too different. Having flown on the E170 as a pax and having spoken with many E170 crews, I know that it is a fine airplane. Those MD90s are not in great shape - the E170 will bring the latest technology and a more comfortable flight deck.
In terms of flying over water, can't the E170s fly over land on the way to the Gulf Region (Dubai, Sharjah, Kuwait, etc.) or to points in Africa (Cairo, Tripoli, etc.)?