Defenses for lvl 10+?

[NecessaryWeevil]

So I often see comments to the effect that beyond level 10, AC becomes increasingly irrelevant unless you invest a disproportionate amount of resources in it. I presume this is because hit bonuses increase too fast?

What, then, are the sort of defenses my Crusader with a 1-level dip in Cleric should worry about, and how should he seek to acquire them, with access to standard WBL and a same-level party member whose effective wizard levels are about 3/4 his character level?

[ComaVision]

Shadow Cloak is a steal for 5.5k

You should definitely have some access to flight.

[Flickerdart]

So I often see comments to the effect that beyond level 10, AC becomes increasingly irrelevant unless you invest a disproportionate amount of resources in it. I presume this is because hit bonuses increase too fast?
That's not strictly speaking true - AC can keep up pretty well with to-hit. The problem with AC isn't that it scales slower than to-hit, it's that it doesn't scale at all. You have to keep buying better gear to raise AC, whereas everyone who wants to attack gets +1 AB per level. So you're spending dosh just to stay at the same place you started.

Also at higher levels, the scariest things won't be delivered through attacks against AC. You will start seeing more and more magic being tossed around, and it doesn't matter how much steel you have between yourself and the enemy mage when that mage mind controls you and tells you to hurl yourself off a cliff. A subset of this is deadly deadly touch attacks, which are much harder to defend against because touch AC is tougher to raise.

The easiest way to protect yourself is miss chance (though try to find non-concealment miss chance to avoid betting pantsed by True Strike). Take the money you save and use it to defend against spell attacks.