Woot! I reached one of my goals: I now have an epic flying mount for my other level 70 character, the priest. I started gathering money a bit over 6 weeks ago, at which point I basically had zero, because I had bought the first epic flying mount just before my break. But I made about 100 gold a day from daily quests, and the remainder by transmuting Primal Earth into Water. So now both of my level 70s have the maximum riding skill and at least one mount to go with it. My warrior already has two mounts, the bought one, and the Netherray. And he is already revered with the Netherwing, so I'll probably continue those daily quests and get the Netherdrake too.
The various mount types are just fluff. But having the 300 riding skill for the epic flying mount makes a big difference for travel speed. And I would assume that the next expansion at least has zones where you can use the flying mount. I don't know if Blizzard plans to introduce further riding skill increases for even better mounts in future expansions. But I have the impression that an epic flying mount will be more helpful in Wrath of the Lich King than any gear I might pick up, because the gear will be replaced by new stuff fast. Riding skill is forever.