I haven't eaten dinner at a Premiere Inn, but I think that their breakfasts are good value and very filling (at least, I do tend to stuff up on toasted sausage butties). I have eaten at the North Terminal restaurants before though.
Joe's Kitchen was okay - staff very nice but I got there late in the evening and many of the menu items had run out (don't know if that's a one off or not, but it left a negative impression).
If you take the monorail down to the South Terminal, then I'd recommend the Giraffe (always a good mix of food so something for all tastes).
1F