We were just talking about this on the podcast last night -- Turpster's tip a week or so ago was that going for the Crusader title in the Argent Tournament actually puts you at a disadvantage, because if you keep from turning in the last Valiant quest for the achievement, you don't lock off having the ability to do both Valiant and Champion quests together, thus, as you can see in the thread, earning an extra 36 gold a day, which adds up to 1000g a month. After you earn the ability to represent every city, you can't do the Valiant quests any more (instead, you have to earn city reputation through the Champion's Writ, which costs you 10g from the opposite reward). In short, right now, if you're leveling through the AT quests, stay away from the Crusader achievement until you have all of the city reputations covered, and all the gold you want.
Fortunately (or unfortunately, depending on how you look at it), Bornakk says that Blizzard probably will make a change here soon to smooth everything out. But how they'll do that isn't quite clear -- they could leave the dailies (or some form of them) open even after you get the achievement, or they could beef up the achievement reward to make up for it. Not a hard fix either way. But yes, until then, you might want to rethink racing to the Crusader achievement, as there's more reward to be had by waiting.