Guess everyone has their own opinion on the subject, I usually go for the high AC characters, anyways, so it doesn't bother me. The reasoning I was under is that if your AC WITH those 3 maxed items is, say.. 32, and a lvl 20 fighter with say a +4 greatsword and a 20 str, weapon focus/Weapon Spec attacks you , he's got a +30 attack. An 'average' Fighter, I'ld say.
To hit you he needs: 2,7,12,17. On average he'll hit you 2.3 times/round.
If, on the other hand, you were to drop each of your items by 1 (+4 ring, +4 amulet, +7 bracers) he now needs : 2,4,9,14. On average he hits you 2.75 times/round. That's .45 hits/round, or an average of say 1 extra hit every 2 rounds.
His damage with that sword averages to 20. So in other words, avoiding an average of, say 10 damage per round costs you 51,000 GP. (And that's only during the rounds that he GETS to full-round you).
Though keep in mind, that this doesn't take into account Power Attacking or any other special attacks, just the straight attacking.
To some people, that's worth it. To me, it's not. As I said, to each his own.
Though looking back at this post, I think I like math a little too much...