First of all, sorry for wall of text, I sorta got going and never stopped XD
Regarding the Spec, I would make a few changes
In arena, your going to want Healing Focus, Desperate Prayer also helps a ton, can be a great oshit button. Focused Power is also a Flat 4% increase to healing, as well as taking 1 second off the mass dispel cast time, which can make a large large difference in arena's that could be the difference of a pally getting a heal through his bubble, and him dying. I would also look into Silent Resolve, it can be helpful because if your against anyone with a purge effect, your sheilds are going byebye for sure. Regarding dropping talents, im not too sure where to drop, that would be up to you, would help if I could see your armory. But some things to help you with on that, Reflective shield is great, but probably not as great as you would think, as it only reflects damage off of you, not your partner. If mana is a complete 100% non issue, you could consider dropping Rapture, But that would be up to you. Also going only 1/2 in Grace is acceptable, seeing as there will only be two of you, so casting a heal or two every 15 seconds shouldn't be that big of an issue. Don't take my advice as OMG I have to change this, just some things to look into.
If your doing two's i would very much recommend a Pain Suppression Glyph over your prayer of healing glyph, as prayer is not a viable heal for only two people, you would be much much better off casting binding heal, It will get both of you with half the cast time and mana cost, and this glyph allows you to pain suppression while CC'd which is AWESOME when trinket is on CD. And I would also get a penance in there, 2 seconds is a actually a lot
Now I'm not 100% sure, but I think you can get furious from the triumph vendor now, so go do some heroic spam, and you could get some easy upgrades. I would advise going Runspeed / stam on your boots instead of the nitro boosts, the run speed helps a ton, and you can't use the nitro's in arena. Also, 1000 resil a decent amount, when you get some upgrades, you may want to consider dropping some PVP offpeices for PVE pieces if you can. I.E. Bauble of true blood (BQL 25m)
And i've never seen or heard of a holy preist in arena' I don't think it would be that effective until you got to 5's. Though it could just be me never hearing of this.
I would advise checking out the website arena junkies, and watching some streams / videos to help see what you should be doing, it actually helps quite a bit