SB Nation's United blog Black and Red United has a comprehensive breakdown of the team's decision to sign Pablo Hernandez here. While the positives and negatives are both taken into account, the main point is that this decision could determine whether general manager Dave Kasper keeps his job.
There are, however, reasons United fans might not be very optimistic about this. Those reasons can be summed up briefly as Donnet, Carvallo, Martinez, Peralta, Niell, and Gallardo. This club has had a terrible run of signing players from CONMEBOL leagues (especially Argentines). In Donnet's case, it was just the wrong formation. Everyone else, though, was either not good enough, disinterested, injured, or some combination of all three. These players generally cost more than most, and we all know about how tight MLS's salary cap is. Botching this many signings has left fans with little faith in general manager Dave Kasper, who appears to be the least popular person attached to United amongst fans. Even if Boskovic was mostly scouted by Chad Ashton (couldn't find the link to the article that said that...if someone can help me out in the comments, I'd be much obliged), the players coming in for this window will probably be Kasper's last chance to keep his job.