They have one of the best products in baseball. One of the reasons they are so successful is that they value winning over PR. They assume their fans are smart enough to understand that signing Lincecum to $20 million/year is idiocy. Maybe that is why they don't go seven years without making the playoffs.
A new stadium would increase revenue to the point where they would keep guys like Donaldson…or not (most the of the players the A's let go have stunk after they left). At the very least it would give them more options for success.