Lightwell - The tank can't take a time out to go use it. Others may not be in a position close to it, or think or have time to use it. AOE damage has to be dealt with quickly, before another AOE takes out the group. By the time somebody thinks to go use it, I would have thrown a renew on them. It's just my opinion, but I can see people dropping dead and me saying "why didn't you use the lightwell?".
Holy Reach would be nice, but I don't want to give up 2 points from other talents to simply increase my Prayer of Healing radius. Usually I find the normal PoH radius to be sufficient.
Improved Devine Shield - Same thought as above. I'd rather have improved healing talents full time. Normally I shouldn't be taking much damage. If I really have agro, a couple hundred more damage absorbed is probably not going to save me. If I was a pvp player, rather than pve, I might go heavier into discipline and spec into this and reflective shield.
Must have for disc/holy in my opinion... Silent Resolve (reduced threat), Inner Focus (any spell when out of mana), Meditation (mana regen while casting), Devine Fury (reduced cast time).
The more you heal, the more threat you generate. I haven't found any one spell to be worse than others. It's more about allowing the tank time to gain agro. Use the appropriate spell at the appropriate time. Start with PoM (agro for the tank) and refresh it when you can, then renew (keep it up), then other heals as needed. Don't spam either PoH or CoH unless necessary. Be ready with it when there is AOE damage.
I'm a fairly standard 24/37/0 healbot build.
Edited, Feb 9th 2008 12:24pm by dadanox