Where do you see these Audi A4 quattro (you mentioned AWD) for only $30k from actual dealers? The 328i and A4 can be had for comparable real world pricing, you aren't saving anything. However you could save money by avoiding the purchase of one the least reliable car brands, that brand being Audi. MPG difference is negligible within 3 points city and 1 point highway, this will mostly be a driver thing especially since you will have to be careful to keep out of boost in the A4 when cruising. The 328i RWD also accelerates faster than the A4 in testing and with its legendary weight balancing it can handle as good or better than the Audi AWD. BMW in its history has never needed excessive peak torque to keep up, it's just great design.

Interior is subjective but by the sales figures we can see that people prefer the 3 series overall.

I very much like Audis but I was raised in Bavaria so I do have a slight bias.