In that context it really doesn't matter how much food can be produced in the close neighborhood, do as other trade intensive areas: let your smart people make a lot of money instead of plowing and buy food cheaply from the stupid peasants elsewhere...
This is exactly how Novgorod lost to Muscovy. Everything was fine and dandy, they (Novgorodians) were buying bread from Russian interior to feed their traders and craftsmen and racking up insane profits selling Russian wares to Hansa and Western wares (and cheaper locally-produced copies) to Russians. It all went on and on until one industrious princely family (Dukes of Moscow) gained control over bread-supplying areas. At this moment Novgorod was doomed. All following events (battles between Muskovites and Novgorodians, siege of Novgorod and such) were little more than grand posturing and both sides knew it. Dukes of Moscow ruled over Novgorod by controlling it's access to food long before they ruled over Novgorod through their appointed governors.
No it's bwenefits in northen climate isn't obvious
Which pretty much kills POD of "corn agricultural revolution in Scandinavia", isn't it? Besides, one more fodder crop (even very successfull) isn't a game changer in medieval economy. What mattered than was what humans could eat, not cattle. You can keep cattle and sell cheese and buy food grain today. You couldn't do it in medieval times.
Edit: I was thinking of "medieval potato" TL for a good long time, as tatters greatly change power balance in medieval NE Europe, giving Northerners cheap and abundant source of starch (as an added bonus, it is extremely resistant to raiders, you can't burn a potato patch the way you can grain field). It would greatly affect not only Scandinavia but also Novgorod, Prussia, Northern Germany, Great Duchy of Lithuania.