Paladin/Sorceror Gish Build

[Caelic]

You'd be better off going with displacement combined with greater mirror image, I think your odds of getting hit by one attack are something like 1/36 between the two.

Alternatively you could go with wings of cover to negate one sucessful attack/round.

Of course I feel that trying to optimize AC is a fool's game after a certain point, though a quickened-extended shield spell that gives you +9 shield bonus to AC is pretty nice for a 1st level spell.

No real reason not to do both--and while AC doesn't count for much after a certain point, it's still nice to have when the opponent has Pierce Magical Concealment and swings for the fences with Power Attack.

[Maat_Mons]

There's an armor modification called ceremonial that you might like if the full plate is only for fluff.  Ceremonial armor is kind of craptacular, but it has the unique property of being heavy armor that doesn't reduce your speed. 

Ceremonial: +1 max. dex, 2 better ACP, no speed reduction, half ASF, half weight, half AC bonus, twice normal cost of masterwork armor, Dungeon 105 p71

So, the statistics for ceremonial full plate are:

• Category: Heavy (but no speed reduction)
• Cost: 3,300 gp
• Armor Bonus: +4
• Max Dex Bonus: +2
• Armor Check Penalty: -4
• ASF Chance: 15% (ASF seems to only go in 5% increments, and you round down unless otherwise noted)

[Rejakor]

Very little provides as good surprise attack protection, before all-day buffs come online, too.

Personally i'm a big fan of multiple layers of defenses, right up and to contingent revivify.

[X-Codes]

I don't think it works, and I don't think it's worthwhile even if it did; the effect would still be too small for the investment of a 3rd- and 4th-level spell.  The big benefit of the Luminous Armor line is the -4 to hit for enemies.  That's an effective buff to your touch AC, which is always worthwhile to keep high if you have the opportunity (and if you're picking up stuff like a Monk's Belt with a Cleric, you should be able to manage it).