Well, Cataclysm - and its decision to prioritize a revamp of old world Azeroth - turns out to be real. Five additional levels, two new races, new class combos for existing races, and massive overhauls to existing overworld zones are all in.
The only trouble is that Cataclysm isn't here yet. Blizzard says it will arrive in 2010, and, based on the patch cycle so far in the Wrath era, I'm going to guess that it will land no later than a year from now. Even so, that's a chunk of time. How will the looming changes affect the value of present day incentives and activities?
Variety for the Alt-o-holic... but not now
The two new races, being the shiny centerpieces of the feature set, are being handed the keys to the proverbial kingdom. Worgen druids are in, with only would-be Worgen Shamen and Pallies left out of luck. Goblins are in, and apparently are spiritual enough to be Shamen, leaving only Pallies (the one combo that would really make me cringe) and Druids off the table.
Collectively, the expansion will add over two dozen new race/class combos. Perhaps the most significant are Worgen Druids, Troll Druids, Tauren Pallies, and Dwarf Shamen, since each of these were previously limited to a single race on their faction. If you wanted to be an Alliance Shaman but just can't stand the Draenei accent, you are currently out of luck. In Cataclysm, you can have an alternative... if you want to wait that long.
Last Chance or First Dance?
It sounds like Blizzard will be keeping the total gut-and-overhaul treatment for zones that are currently vast and sparsely populated with quests/hubs/etc. For example, they said that Elwynn Forest (which doesn't have that much structurally wrong with it) won't be changing much. Other places, like Desolace, Ashenvale, Azshara, and The Barrens are all going to look very different.
This one can swing either way. If you want to see that stuff the way it is today for the last (or first) time, it's now or never. Then again, how many alts do you really want to level? Perhaps you'd rather wait for the new stuff?
I could go either way on this. I honestly don't know where Mankirk's wife is - my one high level Horde character went from Mulgore to the Ghostlands to some combination of Hillsbrad/Ashenvale/Stonetalon and completely skipped the entirety of the Barrens (which I haven't really played in since open beta). However, with all of my alts and heirlooms on my Alliance server, I'm in no rush to sink time into a throw-away alt that I won't be sticking with when the expansion hits. Maybe I'll just ride through on my high level warrior and one-shot all the mobs just to see the quest text.
TBC and Wrath
We have no real indication that these areas are up for a revamp, and you would figure that they have the least need of one. However, there was that pesky rumor that Garrosh will take over command of the Horde from Thrall. That would derail the Wrathgate questline, and the one that introduced Garrosh in the first place in Outland. It's been confirmed that everyone, expansion owner and non-owner alike, will get the revamped zones, which would presumably include the city of Ogrimmar. I'm definitely going to try and do these iconic lines before the expansion, for fear of missing them.
Level 80 gear and heirlooms
Obviously, your heirloom needs/desires are going to vary with your plans for alts. If you're venturing onto the other faction, bear in mind that you will either need to do group dungeon content, max all of the Argent Tourney reps, or do Wintergrasp in order to obtain heirlooms. (I'm suspicious that the currently not-dropped-anywhere Emblems of Heroism may become available through a daily quest in 3.3, but that's speculation on my part.) All of these options basically require a level 80 character.
In terms of non-heirloom gear, the jury is out. With a smaller level cap increase, my gut reaction to the announcement was that Blizzard would go with a greatly diminished gear reset, if any. That would be good if you like to remain on top of the game for longer, but bad if you're looking for solo content that actually challenges you. Perhaps this will be addressed on day 2 of Blizzcon, but it hasn't been touched so far.
My advice is not to change what you're doing because of the expansion; if you're enjoying raiding and happen to collect upgrades, go for it. If you're enjoying 5-mans, even though you're not getting upgrades, go with that.
Other Mechanic Changes
Among other things, Hunters are moving to an energy-like Focus stat and non-consumable ammo, Warlock Soul Shards are getting replaced, a wide variety of specialty stats on gear are getting streamlined or eliminated, and various classes will presumably get various improvements to their quality of life. Then again, there's always something a little bit better down the line, even after the expansion.
What Will I Do?
Overall, I expect to take a Worgen Druid (future flavor of the month, I'm sure) and Goblin Hunter for at least a test drive through the new starting areas. My old Tauren Warrior will get dusted off to see the rest of TBC and Wrath from the Horde side, and possibly Wintergrasp for a gun for the Goblin. My mage will work on the things he was going to work on anyway, and my assorted Alliance alts will probably gather dust for at least the next year.
Overall, it's possible that I will play less WoW total between now and the expansion because I'm waiting for changes. I'm not so nostalgic for the 40's as to try and rush Cheerydeth through to Outland with a revamp looming, and the coming addition of the Dwarf Shaman effectively guarantees that I will never spend significant amounts of time playing a Space Goat. In the long term, though, the reduced time in present-day Azeroth, with concrete plans for characters other than my main once the expansion hits, may prove to be a blessing when I hit 85 within the expansion's first month. It's not like I'm hurting for other stuff to do in the mean time, so I guess that's a good thing.