Should I bother putting three points into mage armour?

Does Dragonhide benefit from this perk?!

No and No.

You are better off in almost every way just wearing armor, but if you want that pure mage feel this is all you get.

I'm doing just fine as a destruction mage wearing robes and I haven't even put any points in alteration yet! Many ways to succeed in this game. Don't just rely on forum opinions. Try and experiment in game!

Yes. Worth it. Ebonyflesh dual cast with sustain perk + Lord Stone = 350 armor for 3 minutes. Plenty strong, plenty long.

Edit: I didn't want to use up perks in an armor tree.

Do it if you want a pure mage, I am going to do it.

If Dragonhide ignores 80% of physical damage I feel that the armor perks really aren't necessary, especially since they don't improve an already powerful dragonhide.

I find that Heavy Armor is superior as a mage with the Steed Stone but the Oakflesh route isn't a terrible one to go if you remember to cast it before you go into battle.

Also Dragonhide is as good as the best armor setup. It lasts 99 seconds with sustain. Can use ethereal shout to have uninterrupted recast during combat if needed. Fighting was us ually done before needing recast, though. Played my mage up to lvl 61. Now I am playing a sneak thief and wearing armor and using weapons. Also fun.

Takes a while to get there, though. Need something till alteration gets over 90. Also having xxxflesh handy when dealing with less formidable foes is convenient.