I'm feeling you man.
Going into BoT with Ilvl 365 is quite boring ^^
Maybe me being such a huge fan of TC is that I absolutly LOVE the fact that a healer damages the boss and actually GAINS something usefull.
I'm also a huge fan of the Atonement Spec of discipline Priest, but its like being in sport class building your football team and the atonement spec is one of those "special kids". Knowing PI to the 17th digit isn't really helpfull if you are looking for a striker.
Also 2set T12 bonus isnt as strong as it sounds. 1% base mana sounds much, but considering that your base mana as a shaman is only 23430 it returns "only" 234 mana.
It takes 2,5 Riptide ticks to proc the T12 Bonus (in average)
Seeing as a Riptide does 8+1 initial ticks it averages out to 3,6 T12 procs
234.3 * 9 * 0.4 =843,48 mana gained
Its basically reducing the cost of one Riptide by 38%. Don'T get me wrong here, it's still a good bonus, but it sounds better than it is.
Also about this haste thing. Don't worry. Haste is in theory slightly better in spam situations, but in actual combat situations the time gained through haste will very seldom be enough to get off another lightning bolt. You will only start casting heals again faster and gain no extra mana
TC scales well with both Haste and Crit. Haste scales roughly 1.87 times better than Crit for Lightning Bolt damage, but Crit is roughly seven times more effective for TC regeneration as it does not increase the initial mana cost
Source
Edit: Also: if you go for a TC oriented build don't underestimate the thought process behind: "Casting LB or Heal". Before it was only "heal" now you have a choice before every cast which can really hinder your heal capablities at first, but with more time you will learn to make these quick decisions.
With TC you need to reevaluate your Spirit. I rarely go for a Spirit value higher than 2,5k (I have 2,2k right now), because Crit/mastery are better for my heals in the long run, because of the huge mana gain I get from TC.
For example Core of Ripeness would give me almost 0 benefit if I use it instead of my Tear of Blood, because in the boss fights right now (BoT/BWD) I have almost infinite mana.