The above poster is WRONG
You can get to 80% damage reduction with the master level alteration spell dragonhide. That's the same as having armor capped.
You can get 80% damage reduction but you can't reach 567 armor, so no, that poster was not wrong, much less WRONG (!!). Sure, 567 armor equals 80% damage reduction so the end result is the same, but armor and the whatever-skin spells last a whole lot longer than Dragonhide and Dragonhide isn't affected by the Mage Armor perks anyway.
Generally speaking, I'd further say that constantly casting Dragonhide is a waste of time when you could just as easily be using a suit of light armor. The weight difference is very tiny and it's loads more convenient not having to constantly worry about your damage reduction running out and needing to be recast.
I'd say you look at the other perks in the trees to make your decision. My mage went alteration for the purpose of stacking magic resistance and the free magic absorption from the alteration skill.
It's not so much a question of the other perks. Mage Armor is crap no matter how you look at it but spending perks on magic protection is an okay deal if you're not planning on spending those perks elsewhere. A pure mage can afford to put a fair few perks into alteration even if said mage isn't going to rely on Mage Armor.