Yes and no. For me I find NG is actually annoying for Wrath - when it procs I have to react quickly to start the next cast before this one has finished (to counter lag), but I end up doing it too early and it doesn't start casting the next one, which effectively means I sit there for a second not casting anything. No benefit at all for me.
It sort of does - haste still reduces the GCD allowing you to start the next cast faster (although see above - same issue).
Haste doesn't change your DpM - it should remain exactly the same. What it does do is increase your cast rate which increases the rate at which you use mana.
Yeah, I noticed the same thing in DTK and Ahn'Kahet last night. Those hurricanes sure do burn through the mana pool... Still, boss fights are the only real concern for maximising DPS / avoiding OOM