I don't see what the big deal is about acquiring Reyes. He's explosive and exciting, gets on base fairly well on a career, and is a dominant player when he's on the field. He's had some health issues recently but when he's in there he's amazing, and he's still a decent bet to play 130 games a year, and the backup we have for when he isn't playing is at least worthy.
Sure we could do fine without him, prolly. We could also do even better with him. His OPS numbers are already good even before you add in that he'd be yet another player with flat out ridiculous speed. Acquiring him would represent a determination to be the absolute best that you couldn't help but admire.
As for known flaws like health and attitude, that'd be the only reason a guy like that would even be available at all, and we certainly have options if the gamble backfires, so the risk is not that high. When healthy the guy is a 5.5-6.0 WAR player, replacing a player who's about 0-2 WAR. The reward there should be obvious. I just think it's an idea worth pursuing.