This is not your first post on the forum, you made one back when you were in your 30's! :D
/wave at fellow Spinebreakian
Ideally, mana pool won't be an issue - you'll get high enough regen that base mana isn't an issue. Seems like this will be more of an issue with ZA than anything else well into 25-mans.
The biggest boost would be grabbing tailoring and going for PMC + WM set, but if your guild is planning on moving onto ZA next patch, there's some stuff that's just slightly inferior and allows you to keep herb/alch. If ZA wasn't coming out, I'd definitely say grab tailoring instead of Alchemy then, and I'd still lean in that direction.
Head: Whitemend, or cheaper alternatives being Hallowed (Arc), Second Sight (Heroic Crypts), or the CE Revered helm. Get Revered with HH for the helm enchant.
Neck: The one you have is good, I'd stick with it till you get one of the Kara ones
Shoulder: Either get Royal Nightseye in them (more healing), or upgrade to Curator ones soon (more regen, and what I'd go with).
Back: One from Sethekk is a minor upgrade, I'd just wait for one of the Kara ones or start farming badges for the PvP one next patch (ever-so-slightly inferior to Prince cloak).
Chest: Hallowed definitely, and gemmed well. If you don't pick up tailoring, that'll last you till the ZA ones for sure (which, btw, are pure awesome).
Wrist: Farm badges for the 2.3 wrist, might not even be worth grabbing and enchanting the Maiden bracers.
Hands: The gloves from Botanica would be a (fairly minor) upgrade. I'd grab those and (once again) farm badges for the 2.3 gloves.
Waist: Get the one from heroic Slave Pens (higher regen) or heroics Durnholde (more stam and healing). If you've got gold to burn, consider getting one of the SSC/TK guilds to make you a Belt of the Long Road (I'd guess around 1500g). Probably easier to get it from Horde and have them throw it on the neutral AH, though I really don't know how Vox or other guilds charge or if they sell them even.
Legs: Whitemend. If you can get into a Doom Lord Kazzak run, there's an insanely good pair that drops from him, beats out WM with the set bonus and definitely without. Get the Golden Spellthread on either of them.
Feet: For regen get the ones from Shattered Halls, for raw +healing get the ones from Heroic Mech. Those will last you till Shade's really awesome ones.
Rings: The ones you have are good. I still prefer the BM quest ring (Keeper's Ring of Piety) over the Violet Eye one until you hit Revered/Exalted. Consider farming the honor for the Season 3 ring as well, it's very good even for raiding (and adds a fair chunk of stam).
Trinkets: Black Morass, heroic badges, or revered Lower City are all good. For a heavy-regen one, there's one from Heroic Mana-Tombs (though be warned that the first boss in a nightmare). There's a fairly good one coming in 2.3 either from Badges or lots of honor (identical except for name), but it lacks the +heal on use.
Weapon: Season 2 mace, or just hold out for the one from ZA. The one you have is good, and might not be worth getting the Maiden/Prince one and re-enchanting it if you think you'll get the Season 2 mace in the next few weeks.
Offhand: There's a really good one from badges now, and another good one coming with 2.3 that's badges as well. What I'd probably do, though, is farm Exalted CE, get the slightly-inferior offhand from that, and save up all those badges you just got for all the 2.3 items. The offhands from Arc or heroic Slave Pens are good in-betweens.
Wand: While it should probably be the last on your list of things to get with all those badges, the new damage wand gemmed with a Royal Nightseye is, sadly enough, the best wand till well into SSC. It's so incredibly marginal over what you have, though, that I'd ignore that.
Conclusions about gear:
Whitemend is biggest and easiest upgrade. I'd suggest farming Exalted with CE for badges and the offhand, and revered with HH and LC (and Sha'tar by default of Mech being really easy to badge farm), snagging as many items as you can along the way while you farm the crap out of heroics for badges.
Spec: I'd drop one point from Silent Resolve and one from Empowered Healing to grab Improved DS. It's a fairly big buff to the raid if you've got many casters at all.
Healing tips: Keep renew and PoM on the tank as much as possible. If PoM pops back to you, you can (very, very carefully) Rank1 SW:Death it back to the tank. Use Gheal primarily if you can, starting a cast and canceling it about 1.5sec into the cast if it doesn't look like the tank will need it. PoM is godlike on Maiden, Curator, and Netherspite.
/the wall of text burns my eyes!