I'm of the opinion that KOTR was one of the WWF's better PPVS and did a lot to advance the careers of most of the winners (excluding the obvious mis-steps of Gunn and Mabel).
Bret, Owen, Austin, HHH, and Angle all immediately benefited.
Lesnar's win would have been better if they hadn't had the stupid "winner gets a title shot at SS" stip. That was the deathblow of the tourny as far as I was concerned as it completely telegraphed the winner, plus they fucked up by trying to make the RVD-Lesnar feud a big deal when nobody was really buying into it. They REALLY blew that PPV.
Shamrock had been in the midst of a fairly long feud with Rocky at the time of his win, and as much as you can say he didn't advance past IC Title level and that Rock should have got the win, he was MAJORLY over at that point in time and the final match against Rock got HUGE heat, PLUS Rock was put over huge due to the nature of the finish. That match was really the start of Rock's face turn and it came soon after, I don't think Rock winning was the right booking at the time. Shamrock always got heat, I think the WWE dropped the ball with him more than anything, turning him heel and putting him in the corporation (in a tag team with Bossman no less) shortly after winning. Anyone remember his three way team/feud with Mankind and The Rock that summer during Rock's brief face period before turning heel again at Survivor Series? Shamrock was mad over.
Edge didn't get his huge push until 2002 with Angle, but at the time of KOTR he was still a tag wrestler and the win was the impetus for his breakup with Christian (remember Christian being jealous of Edge and wanting to carry the trophy around with him all the time?). So in that regard it was an important step in breaking them up and moving Edge into serious singles competition, even if the benefits were staggered a bit.......
I wish they'd bring KOTR back, they have a TON of young talent who could really benefit from being put over in that format and getting to brag about being "The King" for a whole year (see: Owen Hart, the guy's "King of Harts" gimmick was classic, classic heel work).