If you have never done any thing there its worth some time..but the only real xp is from quest turn ins if your at 80 plus.
There's the argent horse mount you can buy but that's after you complete all your factions quests and become exalted with all your cities (except worgen or goblin) and it opens up a vender in the Argent tent..It cost 150 champion seals which you can start to obtain before getting the vender to sell to you and that same vender has some BoA gear.
But at least doing the one time quests and maybe getting through one of your factions is worth it IMO.
( EDIT) Forgot about the pets.. but each city has a unique colored mount as well, so like everyone said unless your into experiencing all you can pets,mounts and achievements are the only real reason to do them.
Edited, Dec 3rd 2011 2:58pm by ChiefsClassik
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[wowsig]2609911[/wowsig]
WoW
90 Orc shaman
90 Orc Hunter
90 Troll Hunter
90 Dwarf Hunter
90 Undead Warrior
EQ2-EQ1
Scrappy 92 Ratonga Bruiser
Mazum 91 Kerra Ranger
Daktari 65 Iksar Beastlord
DragonFists 71 Iksar Monk