I've got cruise control on mine, the mpg is slightly reduced when using it as opposed to controlling the speed yourself.
I quite fancied and A4 when I was looking but the Passat was a cheaper option and still a good car. The Interior isn't as nice as an A4 but it still has all the refinements you need. I think the Passat has mpre space in the back than the A4. Not sure if its an A4/A6 hybrid in terms of size.
I had a 97 passat saloon before the A4. It had way more space the my A4 and it's an avant. I'll have to see where the pennies are when it comes time to change. I don't mind high mileage and if I can find a high spec Passat I may just go for it.
I do love m AUdi tho!