I made a little addon that says in party chat why a spell failed (If you are the party leader, nothing happens).
For example:
[Party] [Wyvrnsheart]: You fail to cast Renew: Not yet recovered.
Anyone wanting to improve on this idea is more than welcome to it. I dont have time to really get into lua programming right now.
Sounds cool. But I used MSBT to report everything my alternates are seeing. You simply have to find out the right channel such as PARTY_SPELL_DAMAGE (may be wrong spelling but you get the picture), and then it will help you parse the sentence and report the way you like.
I have a setup that tells only how much dmg my warlocks do. The original sentence I see on my tank's screen should be CharA's Shadow Bolt hits BeastB for X amount of dmg. But it turns out to be CharA: X on my screen. Very neat and tidy.
You could find that addon on Wowinterface.com I suppose.