Is that Raz or Rossi? I can't tell.
Is there any reason to do all of the pre-Cataclysm quest chains on all my characters at this point? Or even my main and my highest alt? Like, do we know if we'll get some achievement or reward for going through it all or not?
Not really. The chains are cool though, and they're worth your time if you want to pocket around 150g and read a good story. I personally did them on the druid I was leveling at the time and got a fair amount of XP.
If you kill each type of rift, you also get a feat of strength, Tripping the Rifts, for your efforts.
The Raven asked:
You said Hyjal and Vashj'ir have a required minimum level of 80. Can you not access the zone until 80, or the zone is way hard for a level 79?
As cutaia pointed out, the quests won't be offered to anyone below level 80. You can still fly over the zone, etc. ... but no quests.
Is the Argent Tournament still going to be going on in Cataclysm? Will there still be a reason to do it?
The Argent Tournament will continue to run during Cataclysm. I suspect that some people will continue to run it, mainly to get the pets, mounts, and other unique rewards. It might be hard or impossible to find a group to kill the level 80 elite, but at 85, you really should be able to kill that on your own ...