I was there last year and actually lived in cape cod for 6 months a looooong while back. Few tips as it's a bit scant in the memory...
They have a standing section at the back of Fenway which is easy to get to for the bar etc, depends if the game or a few ales is your primarily objective. Being stuck in the seats for 3 hours isn't fun if you want a get a few beers in and constantly need a piss.
I can't say there is a stand out place to visit in Boston, there are lots of nice places and old buildings to have a mooch, it's a nice European style city, just have a wander and you will enjoy it.
Maybe a whale watching tour is the main thing that's different? Also there is an abundance of Lobster/seafood on that coast so that's the place to eat it.
Cape cod is very nice, but it's probably too far if you are only there for a long weekend, if you were there for a week I'd say go there.
Also stay away from the 'combat zone' which is the titty bar area, rip offs are abundant.
Enjoy
