I don't know much about Young's perceived attitude problems but what he does lack is an ability to go past players. He's extremely quick and fairly comfortable on the ball, but he's not going to give you the dimension that a Robben or a Ronaldo give with their ability to scare the shit out of the defenders they run at. Which is obviously why the likes of Hazard and Sanchez are so sought after as they're probably the best bets to be the next Robben/Ronaldo.
Having said that, what Young does offer is pace, width and a consistent supply of crosses from the wing. He is quite easily one of the best crossers of the ball in the PL and I can see Carroll benefiting tremendously from that. As for the concerns about his lazy work ethic, I can't profess to know much but his stats over the last 5 years have him averaging 10 goals and 10 assists a season. If he can be as consistently productive for us, he'd be excellent value at about £12m.
There's a lot of speculation about the owners spending really big in summer, and although I think we'll see a net outlay of about £30-40m in the summer, it'll probably be distributed amongst 3-4 signings. It's too much to expect them to splash £25m on a player like Hazard/Sanchez when we so badly need enforcements in areas like CM, CB and LB. Signing someone like Young for around £12m might represent the adquate compromise in addressing the need for a winger with a well established and quality PL performer rather than a potentially world class winger.
If we are to get that potentially world class winger, it'll have to be through Comolli spotting a cheaper and more unestablished talent. The likes of Wijnaldum or Boudebouz perhaps.