The thing with Martin is that since his very first day, his shot has been improving, and he's been becoming more aggressive when it comes to creating/exploding to the basket for himself. I see no reason why it won't continue next year.
As for Collins, he went from looking lost to being a very respectable center by the end of the year. He played very smart defense against Shaq, and has a decent jump-shot that he can use more. He will be much improved next year, in my opinion.
As for Detroit... as streaky as Billups can be at times, he's a significant upgrade over Chucky Atkins. He's also automatic from the line, which means that they should have more success in close games, because he's a 90% free throw shooter.
Even if White or Okur don't do anything, the increased role of Rebreca to go along with the signing of Billups is enough to improve the team, in my opinion.
As for Hill.... yea, I agree with that. If he's healthy, he's the biggest acquisition in the East. Although I still don't think their interior defense/rebounding will be enough to make them better than Detroit or New Jersey. (although if Hill is healthy, and their big men don't look foolish... I wouldn't be surprised if they finished third)