The 13% spell power is huge, for a caster team.
Even if you were to never manage Eclipse, and go with straight Wrath or Starfire.
The 13%, makes it worthwhile to have the toon on the team.

I converted (traded) a shaman from one team (giving the new team a 2nd shaman) for a warlock.
The warlock has fresh to 80th, literally in more greens then blues.
I gained a 2100GS (warlock) for a 4000GS (shammy)...
And the teams overall DPS significantly increased... heroic fights that I was very close to winning became easy with the trade.
Now the entire team (warlock too) is in full T9 badge gear.

If you had another source of 13% spell power...
An Unholy DK tank or a Warlock instead of the mage perhaps.
I'd consider Druid as healer, Priest as dps.
But for the above classes... approximate the Eclipse.
I like Mercurio's suggestion.. 2x Wrath to 1x Starfire, I'll try that on my mixed team.