It seems that Aer Arann are filling in a few spaces quite nicely. ORK/EDI should be a good route for them. As should GWY/STN.
I agree with the DUB/NCL route. Now that BA only use the Jetscream 41 because of the lack of competition, I think the presence of an Aer Arann ATR would soon see the passenger choose wisely. I believe Gill Airways ATR's were giving the Brymon Dash 8s a run for their money on the route when they competed, just like they did on NCL/BHD. BA left Gill to the route after about 12 or so months of miserable loads. Need to keep the fares reasonable thought mind! They would poss nick a lot of leisure traffic from Ryanair at Tees-side if that were the case. Ryanair have recently increased frequency on MME/DUB at weekends - probably because of the poor service by BA from NCL.
As for Dublin - Rennes. It does seem an unusual pairing. Must be a reason behind that one. Perhaps ferry traffic is substantial?
Luton - Cork could well be a fabbo route. Waterford is much smaller than Cork and like you say, it manages 2 daily rotations.
