Assuming you're in the appropriate level range, yes! There's no threat of a bunch of Horde zoning out of the Stockades in the middle of Stormwind because the tool drops you back where you queued, not outside of the instance. It's a good opportunity to see content that normally would have been incredibly difficult to access.
"How do you handle many whelps?"
Run directly into the middle of them and spam all of your AOEs while everyone else in your party also spams their AOEs and then get disconnected due to the obscene data flood.
That's how my raid's rogues seem to do it, anyway.
"When Cataclysm hits, we (our 80s) won't be able to go back to the 'old world' becouse there will be "new old world." Will it be posible to help someone level up in old world? Will I be able to make the Loremaster achievement? Also, will chat channels be separated for old and new 'phase' of these zones?"
There is no old world and new old world. There's no phasing, there aren't multiple versions. When Cataclysm hits, the old world will change for absolutely everyone, even people who are leveling their very first character and only own vanilla WoW and none of the expansions. Azeroth as we know it now is going away permanently.
So yes, you can help someone level, because they'll be seeing all of the same things you will. We don't know what's going to happen with Loremaster yet, but it will most likely be updated to reflect the rest of the world. That, or we'll be given a new one.
"If the Dragons are all children of the individual aspects, where do the proto drakes come from? A lot of them match in color to the various flights, but I would think that Alexstrasza wouldn't let her kids just be hanging out in Northrend, not after what happened at Grim Batol. Also, where in the evolution chain would they be? Higher than whelp, lower than a full Drake? Proto is defined as 'first, earliest, original' so would these be less evolved versions of the Dragons of Azeroth? If so, why didn't they evolve with Malygos, Alexstrasza, Neltharion, Ysera, and Nozdormu?"
The Proto-Drakes are what the dragons were before the Titans raised them up. They were more or less just beasts, like any other thing in Northrend. The Titans empowered many of them (not all of them), and they made the Aspects and the Dragons from them. Dragons and proto-drakes are two different things now, but at one time they were the same.
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