it might not convert every fan, but if it converts some, that's a win. They came and saw a solid game where two good teams slugged it out. They saw we played a flowing, attacking style. They saw we have an excellent player in Nico, even if he's not known the world over. If they want to see professional soccer in person, maybe coming to a NYCFC game might not be a bad thing. It gets the ball rolling.
No, you aren't gonna convert the snobs. But you can convert some casuals who came just because they heard of messi.
Having a big name might fill more seats for us while they are here and if they actually produce, but it would take a pretty big name. Look at NJ. They've got two players with some name recognition yet they can't barely fill a 3rd of their stadium. I think we have pretty good fans to be able to fill 20K+ on average nearly every match, in baseball stadiums, at not bottom dollar prices, and not have a single star with global name recognition.