Death is death...and that's that. :P

If you died please stay down ^_^

But seriously, why should these characters come back?  Wouldn't it have greater affect if they stayed dead?  Death shouldn't be a gimmick.  Otherwise, you might as well write everyone as a Mary Sue because they can't die or won't stay dead, anyway.  I want something permanent.  You want to know why 2nd and 3rd tier characters don't evolve past those levels and layers?  Cause there's no room for them to do so.  For the past few years, everyone's been talking about Trinity this and Trinity that.  Well, let's see how DC can handle the so-called Trinity when one-third of it is wormfood.  Let the dead rest...It's why I dropped Marvel's X-titles, no one stays dead over there. ;)

B.
I don't mind resurrections as long as the writing is okay.

Okay... 
 
1) What signifies a good idea to bring a character back? 
 
2) What signifies a character as being important/popular enough to bring back?

Most of the characters that were killed off died because they weren't that interesting to begin with or in a rare case their character was fully used and had nothing else to really offer. So bringing them back? Not necessary. I liked Martian Manhunter alright, mostly from the TV series, but other than that I'm fine with the dead staying dead. If they really super feel the need to bring the characters back, well, I suspect a major comicwide retcon is bound to happen within the next 5 years anyway so just wait for that.
 
Now, my suspicion is they won't stay dead. They'll turn into some ephemeral passive beings that are 'around' but can't tangibly help or hurt anyone in the universe, or they'll be sent to some other dimension or something and from there the crowd favorites will find a way back. 
Actually yeah, if I had to put money down, the black (and white, later on I assume) lanterns (including Superman as the first WL, just my assumption here because he's out of the league) are trapped in some other dimensional rift because they're all essentially immortal. And from there, good and bad guys will "find a way back" based on reader feedback ie "bring back Batman or else", etc.

Some should come back. Such as; Aqua Man, Hawk, Blue Beetle, and Hawkman(even though he's a given).