Rooney has world class ability though, that was clear to see following Euro 2004. Whilst his game may have changed since then he's still one of the best strikers in the world (when on form)
I dont think Carroll has ever shown the potential to be world class tbh
This is the problem with most fans, not every player who can't do everything, is worthless. Not every player can be Messi or Ronaldo, that doesn't make them useless to a team.
Carroll is a very good goal scorer, he's the third highest scorer in the league in his first season, and he's missed a month due to injury, he's scored 3 less than Tevez, but 2 of those were penalties. Potential, coupled with the club not wanting to sell and the player not asking to leave = huge price.
Rooney may be great, personally I think he's only had a couple of "great" games this year, last year he had a great goal scoring season but he didn't look close to himself. He's mostly a withdrawn striker who likes to get involved, he's involved for 90 minutes but often won't score, last year he was often uninvolved for 89minutes, but also frequently scored.
Theres a handful of players in the world who do both at the same time, Rooney's dropped back to be more involved in the entire game, and his goal scoring has suffered.
Personally I don't think he's world class, his passing isn't fantastic, he has a MUCH better cross than most people give him credit for, he has a ridiculously powerful shot, but he's not a natural goal scorer, he's a ridiculously powerful runner but isn't known for his Messi style dribbling. Theres lots of things that are only average in his game.
The point is, different players for different roles, not every player has to be able to dribble through the entire team to win a game, nor defend, nor cross.
Carroll is a good goal scorer who has shown huge potential for a long career of scoring lots of goals, I would suggest that would make him well worth buying as a long term goal scoring player. Buy someone else to do the rest, thats how football works.
What if Carroll goes to liverpool for 35mil, scores 15 goals a season and never changes club, plays for call it 13 years till he's 35, that would mean 2.7million a year for him. Good value, thats the potential you're buying, and thats the price Newcastle associate with that potential, because they saw him as a player who could score 15+ goals a season, for 10-13 years for them.