I never used the abilink stuff, but that sounds awful. Summoning people is cool though, I liked getting to see all my friend's characters. Late game they aren't very powerful anyways, I just used them to keep my chain going for buffs. You do have to exercise a bit of restraint with them early on though since they can take out bosses in a hit. In the end of the game I think there's some neat pay off for the street pass stuff.
The Norende stuff was weird. It was kind of cool in the beginning to get those overpowered weapons, but I don't think they stayed overpowered long enough to make a difference after like the first half of the game, and you still had to be smart with those weapons in most boss battles, so it didn't feel like it completely broke the difficulty for me or anything. Though it was really disappointing to start stealing end game stuff from bosses only to find out that it was worse than the high level Norende stuff.