While I'm obviously not an expert on this topic, it seems like the parking/transit is going to be a nightmare at the new park. The situation seems worse than Nats Park in terms of available parking, entry/exit points to highways, and traffic flow. However, at least the Nats have the DC metro, which is one of the most efficient and widely used systems in the US whereas Miami has hardly any public transit to speak of.
This sounds like it could be a lot worse than the Nats Park problem. When I went they had us park at JFK and a shuttle took us right over to the ballpark.