Re: Average mpg for Brera 2.2?
Doing 70mph on the motorway in my Spider gives around 31mpg, slightly more on A/B roads if driving carefully. As SR says, it can be economical if you are careful, less so if you're in a hurry. Much like any other car.
Having just googled "cruise control fuel consumption" pretty much every hit suggests cruise control is more economical than trying to maintain a constant speed using your foot. I think the issue is that we're not comparing like with like. If you are trying to get from A to B at a constant speed then cruise is likely to be more economical because it avoids the little acceleration and deceleration that is inevitable if you are doing it yourself. More throttle happens on a hill because otherwise you slow down. You'd be doing the same thing trying to maintain constant speed using your foot.
If you want to get from A to B at a not so constant speed then you may be better off using your foot because you can slow down a little up hill and speed up down hill, so saving fuel. That said, I think you'd need a pretty undulating road for it to be more economical overall because you are still going to be inadvertently changing speeds on flat sections which is less efficient than staying constant.