Also, grinding honor points will be a lot easier/faster in WotLK, meaning there's no real value in saving those either.

If you have epic flyers, maxed out tradeskills (including inscription comps if you want to get that when 3.0 hits), gold to level your tradeskills post-expansion (I'm guessing it won't cost all that much if you have the gathering skills yourself), gold to buy your frost-mount-skill-thingy (currently I think it's a quest + 1k, which you are likely to have from levelling anyway) there isn't much to spend your time on which will last in expansion, but that doesn't mean you can't have fun just playing around, raiding, having fun with guildies, pvp'ing, doing instances, whatever kills your potatoes :-)

If you're into the economy-game you can do that as well. Mats from disenchants will be cheap until people start enchanting their gear at level 80, meaning you can buy them up fairly cheap from about a week after launch until people start getting gear worth enchanting (raid gear, pvp rewards etc) at which point you can sell it and make a nice profit. Lots of similar situations exists that you can use to your advantage and in turn lessen the money-grind for port-rings or whatever moneysinks they introduce.