Not a bad trade at all for the Wild.
As was mentioned already, they got a younger guy who can play any forward position (granted, C doesn't seem to be his strong suit), and since they both are on expiring contracts, and the Wild seem to be doing "auditions" for what they will try to build moving forward, this seems reasonable enough.
I completely agree that on the whole, Staal has had the better career and is still quite serviceable even now.....but he isn't, at age 35, in the Wild's long term plans.
So in come guys like Bjugstad (who Minny basically got for nothing) and Johansson to see if they can pick themselves up in an upcoming season where not a whole lot is expected from the Wild, and if they fail, then the Wild simply wave "bye bye" and continue on with their younger guys or looking elsewhere for veteran help.
For Buffalo, they will be getting a still-solid center who can take a bit of the heat off Jack Eichel either as a 2C or 3C. That will depend upon if any younger Buffalo center can take hold of the 2C spot or not.
His numbers are declining, but don't count out one last burst out of him, especially in a contract year if he intends to keep playing after, after finding himself on a new team that wants to make it to the post season.
Besides, other than Buf's top line, the forwards are very heavily offensively challenged, so any help....anything Staal can give them..... would be extremely helpful.