Agreed with you on the last point. From what the fans have said there will be fanzones.
Your third point, there's 4 years to come up with a traffic plan if required. The stadium is not opening tomorrow. Temporary traffic lights for football games could be an option.
Of course no-one is going to walk to Westhill for a pint. Throwing in a comment like that nullifies the good points you make.
With safe, free flowing traffic leaving the stadium (should not be an issue in 4 years time), how long do you estimate a bus journey to Dyce? It's not like the next bus is going to arrive in an hour. If it's anything like the few buses they have near the top of Merkland road that take you in to town, they're almost out of sight immediately after the final whistle.