The reason people love the draft picks is that drafting great players is how you win championships. Seriously, take a look at the list of NBA champions this millennia. Lakers had Kobe, Spurs had Duncan, Heat had Wade, Cavs had Lebron, Heat had Wade again, Celtics had Peirce, Mavs had Dirk. Virtually every NBA champion has had at least one truly elite level player drafted by that organization on the team. Drafting a player like that has several advantages over acquiring say a 27 yo old veteran. 1) Those veterans are very rarely available, and for what you give up via trade it makes it hard to build around them. 2) They get LARGE contracts that ruin financial flexibility. 3) They are older and the window you have to win is shorter.
The bottom line is that when you say that its unlikely a young player will reach that superstar level you are right. But just the chance that they COULD is immensely valuable, because if they do you immediately become one of the few NBA teams capable of building a champion.
In our specific case the attraction is that getting Paul George doesn't make us a championship team, adding George and Hayward MIGHT, but it not financially sustainable. The freak accidents of the Cavs getting the #1 pick 3 out of 4 years and the huge cap spike allowing Durant to sigh with GS have created two super teams, which the new CBA makes hard to do. In other words people like the youth because even if it doesn't give the Celtics the best chance to win next year, it gives them a MUCH better chance to win in 3,4,5 years.