You always need to analyse the number of attack routes, too. Sometimes two border countries are connected to only one country of the other continent, so its a primary target, it makes the continent much easier to hold. In other cases, its more difficult than it seems. Europe, for example, has 4 border countries and can be attacked from 6 places. So, number of borders isnt THAT important.
Well...
Northwest: no reason for the connection between Wilkin and Stevens. 5 border countries are a good number, even to a 7 bonus.
Northeast: it seems good, but if you want drop a connection, the better one is Aitkin / Cass. 5 is a high bonus. It should be 4 at maximum, maybe 3 (if you drop the connection)... Hmm, 4 is better.
Metro: I suggest you drop the connections: Chisago (is this name right?) / Pine and Dakota / Rice. Its connected to all other continents, so 4 is a good bonus.
Southeast: it really needs be more difficult; I suggest a connection between Steele and Martin. After that, bonus of 4.
Southwest: drop routes from Stevens, and add Martin as a border country. After that, hmm, I dont know. The bonus should be between 5 and 6...
Thats it.
EDIT: I hadnt seen the updated version, I was writing about the ancient one. But you did almost all I suggested.
