When was the last time Barca failed to perform in a big game though? Even the cup final they bossed and Real hit them on the break whereas their away record in Europe is surprisingly average. Not saying your theory is totally incorrect but more teams in the champions league have had joy against them when they get to play them in front of their home fans
So why would you have a better chance against them in a two leg match of which one would be infront of Barca's home fans? Simple fact is, every team ever, and every team that ever will be will have bad games, the best teams don't have many, having two bad games in the space of a couple weeks is even less likely.
Who cares, I was mostly replying to the other idea that somehow strengthening to beat one team was stupid, if it happens to be the best team, its a daft suggestion. If I was a Utd fan I'd be flat out angry if Fergie said "meh, I want to be as good as Bayern, maybe Inter, but why bother trying to be as good as Barca". Trying to be the best is what he should be aiming for.
As for ultra negative tactics, its worked once in 100's of times against Barca, even then it was by the single most defensively minded manager, with two of the best centrebacks in the world over the past decade, with a very well drilled hard working midfield all working for defence. The only teams the genuinely beat Barca are the ones who go and attack them.
Inter played defensively because that was their game, practiced for it, played every game like it, they played to their strength not ultra defensive for one team. Playing to your strongest team/formation/tactic is when you're at your best, playing ultra defensively when the team isn't practiced, or great at it, is literally choosing to play no where near your best, what good is that.