If you miss that much vit you're screwing yourself on all the other item slots where you could have had AR but instead need vit now. Unless you're content with having mediocre dps...then it's a piece of cake to get all the vit/res you need, anyway.
I don't want to sound cocky but if you've tried getting a char to top 20 dps or top 50 heroscore, you probably know what I mean. You get most of the res you need from items that have it by default (zuni pox,vile ward,etc.) or from set bonuses (2 item Zuni) so you don't have to pay obscene amounts for something you can get cheaper in another slot.
You need near-max on the primary stats and on vit for the specific item. If you can get that and AR from the same item than indeed it's a good investment but paying for AR with a ton of gold AND a ton of missed stats is not a great idea.
Your logic is sound if you do not play a WW Wiz, or want the DPS boost from Tal's armor. Kesteg's runs a WW Wiz, so AR is most definitely better than Vit for him. All in all most Wizards will sacrifice Vit for AR/DPS. Even with 8% it is probably a 6-7K DPS upgrade over a comparable Zuni's. I know, because I have one of each. IF I wanted to run WW in the most effective manner this chest piece is pretty darn good especially with the AR.
On a second note, would I personally pay 200+ mil for this piece?...No. In my mind it is a 100 mil IGG piece. If it had amazing stats to go along with it I would pay 250+. If it had 9 IAS and amazing stats it could go for over a billion.
One last note, Tal's is BiS for every class for DPS. Just like Inna's pants, it has something no other item has. A DPS gain via added IAS. The only exception might be a DH cloak with a specific skill enhancement.