Before we bought our D200 I had a conversation with a coworker (who is a professional photographer). It went something like this:
Me: I'm looking at a new D5100, because I like it more than a used D200.
Coworker: What do you like about it?
Me: I like that it's got the same image sensor as the D7000. I just wish it had the build quality and manual control dials of the D200.
Coworker: So why not just get a used D200?
Me: Because...um...it's six years old? Wouldn't a newer camera take better pictures?
Coworker: So, you're saying that six years ago people weren't able to take good photos?
That's not to say a newer camera wouldn't have better features, but I honestly couldn't think of any actual reason why a D200 would not meet our needs. And after having the D200, I would take it any day over a new D5100. However, back to the original point of this thread, perhaps there are some really good reasons OpieCunningham wants a newer model instead of his D200. And if the D200 really doesn't suit his needs anymore (such as wanting better high ISO performance), then yeah, it might be time for an upgrade.