Getting back to Spezza as a #1 centre, his weaknesses on draft day were skating and defensive awareness, his offensive potential was obviously never in doubt.
Sens took the slow road with Spezza giving him time in the AHL and 4th/3rd lines in Ottawa to work on his weaknesses and having seen Spezza play all games last year and a few this this year in the AHL, I think you'd have to be pretty biased to call him slow. His skating has improved tremendously to a point where I'd say he's no worse than Bonk and might be better. It might be just the AHL but in the games I saw he just blew by everyone on a few occasions.
Defensively, his +22 last year certainly was helped by playing for Ottawa but still attests to his efforts to improve that aspect of his game. I don't think he'll ever become a defensive specialist à la Yzerman or Fedorov but he's no longer a terrible liability à la Pavel Bure either.
So, no longer hampered by weak skating and non-existant defence, Spezza's ability to fight through the opposition's best defensive line is the only thing that could prevent him from being a #1 centre next year. He still dipsy-doodles a bit too much but maybe getting back to the NHL he'll simplify his game again, and as long as he depends on his vision rather than dipsy-doodles to create chances, he'll be solid.
Basically Kovalchuk has been the better player thus far, he was thrust into a leading role and ran with it.
Spezza came from further back, had to work on his skating and defence rather than let his offensive talent show but IMO there's nothing holding him back any longer and in the next 2 years we'll see him emerge as an elite centerman, whether he can reach Kovalchuk's level remains to be seen but don't be fooled by his first 2 years, the talent is there he was simply given different assignments than Kovalchuk.