Miller wouldn't be a "meh" loss. He's a player we NEED to become a solid contributor at some point in the near future. We need good players on cheap contract and our prospect pool is thin enough already.
Also, swapping Hagelin for Spezza increases our cap commitment by 4.5 mil, but doesn't add any players. That means one of Stralman, Zucc, Staal or Brassard are also gone, unless you plan on trading Nash.
Trading for Spezza just isn't a good idea.
Yes and no on Miller. It would be cake if he turns into Dubinsky, which is what I think his ceiling is, but we have a lot of center prospects in the wings that can hit that 2C form. Mostly Lindberg and Boo. Fogarty can end up being a good bottom-6 center. Not to mention you can basically find a 3C ever year on the FA market. Our prospect pipeline is sure as **** thin, but that's what happens when you're in win-now mode. Like it or not, that's where the Rangers are.
Miller doesn't make or break this team by any means. I definitely agree that we need good players on cheap contracts, especially ELCs. We have to start getting some bang for our buck no doubt about it.
I have already come to terms with the fact that unless he takes a hometeam discount, Stralman is gone. But it's not like the cap works in a vacuum as you've displayed in your post. There are other ways to finagle cap room. It's not like, oh we're gaining 4.5 with Spezza on the books after trading Hagelin, and that's all the room we'll have to work with. Then Spezza leaves the books in a year, and there's your room to re-sign Staal. Cool, right?
Trading for Spezza is a good idea, pending the price and assets to which it takes to get him.
Trading for Thornton just isn't a good idea.
Signing Stastny to a huge contract just isn't a good idea.
Trading for ROR is probably a good idea, but holy hell, if you think Spezza will cost too much, let me tell you something about trading a proven 23 year old 2C.