Q:

Optimizing spending 52,000 gp on new equipment for a level 13 magus

We just hit level 13, and are going to sell all of our loot, which will net us each about 52,000 gp. 
I am playing a Magus (dexterity build) with the following stats: Str 10 (+0), Dex 20 (+5), Con 14 (+2), Int 20 (+4), Wis 10 (+0), Cha  7 (+0). 
Above stats include bonuses from my equipment, which is:

Scimitar +1 keen spell storing
Mithral breastplate +1 with mithral armored kilt (GM ruled that if made of mithral it wouldn't increase armor weight)
Ring of Protection +2
Amulet of Natural Armor +2
Cloak of Resistance +3
Belt of Incredible Dexterity +2
Headband of Vast Intelligence +2

In our strange group I am playing the role of a frontline striker, using my spells to aim at the strongest of the enemies, and now I really need to reinforce a bit. 
My current idea for spending those ~52,000 gp are:

Celestial armor (22,400 gp)
Ring of Arcane Mastery (20,000 gp)
Belt of Incredible Dexterity +4 (12,000 gp upgrade)

With this, I would net +3 to AC (from 27 to 30), +4 arcane points, +1 to reflexes/attack/damage and a free fly once per day. 
However I am not really convinced by the celestial armor: spending 22k for a +3 to AC seems quite much. 
Another option would be this:

Belt of Incredible Dexterity +4 (12,000 gp upgrade)
Headband of Vast Intelligence +4 (12,000 gp upgrade)
Ring of Protection +3 (10,000 gp upgrade)
Amulet of Natural Armor +3 (10,000 gp upgrade)
Cloak of Resistance +4 (7,000 gp upgrade)

This would net me +1 2nd level spell slot, +1 skill to max rank and +1 to all saving throws, but I wouldn't be able to add more dexterity to AC since I am at the limit already. 
Which of these two options would be better for a melee build?  Are there alternatives which I grossly missed? 

A:

A tool I discovered quite recently to check how balanced my character is is the table in the automatic bonus progression rules.  It tells you, considering your level, which items that give basic bonuses you are supposed to have. 
For a lvl 13 character, it gives:

Mental prowess +4/+2
Physical prowess +4/+2 
Resistance +4
Toughening +2
Deflection +2 (since lvl 10)
Armor attunement +2 (since lvl 9)
Weapon attunement +1/+1 (since lvl 8)

Which means that as a lvl 13 character your could be expected to have (I omitted the stuff you already have):

better ability enhancing items (maybe a belt for dexterity and constitution) (upgrade your item for 6Kgp for the +2/+2, 12Kgp for the +4, 36Kgp for the +4/+4 (maybe this one is a bit expensive right now but you can technically afford it))
a Cloak of resistance +4 (upgrade yours for 7Kgp)
a +2 armor (upgrade yours for 3Kgp)

Of course these are just general guidelines.  Considering your role you may not need mental enhancements beside intelligence for example.  Or need a better scimitar so you need to spend less arcana to hit your enemies. 
If you have already all these items, you can anticipate the next line, for level 14, and get an even better armor, cloak or weapon, or go for more "exotic" items (which I personally recommend, just because the game is often more balanced that way). 
Among these "exotic items" you can go for:

Stocks of diamond powder for when someone will die, or other expensive components
Scrolls, wands, or other magic stuff that makes you better at casting spells.  You may not be the magic guy here but outside fights you will be happy to be able to cast spells without having to burn your arcane pool. 
Skill enhancing items.  You probably have that one skill you are the best in.  What about making it really good without having to spend a feat of it?  Depending of the skill you are looking for it can be very cheap. 

/!\ A Quickened Metamagic Rod may look great, but is not so much for a magus needs one free hand to use Spell Combat.  Using it efficiently becomes quite complicated.