A very common complaint among healing classes is that upgrading their gear only helps them in one area of the game: raiding. This is in contrast to the DPS classes, where raid gear is often just as good for PvP and farming as it is for raiding.
Perhaps stepping back a bit will provide some perspective. As a caster levels, you often find gear with very specific bonuses: +Fire, +Frost, +Shadow, +Arcane, +Heal. However, as you get closer and closer to 60, the more specific bonuses tend to get subsumed into +damage/heal. At 60, there are essentially only two categories of gear that makes your spells more powerful: +damage/heal, and +heal.
So the gear naturally gets split up into two categories. Damage casters go for +damage/heal, while healers go for +heal. The problem, though, is that +heal does not help you pvp or solo. So healers would also like some +damage/heal gear to make them more effective in non-raiding situations. This starts fights with the damage casters who see +damage/heal as their gear, and healers being in less "need" of it.
Now, imagine if +heal had also disappeared as endgame approached. Or that you wake up tomorrow and every +heal bonus on epic items has been replaced by the equivalent (lower) amount of +damage/heal. What would that change? Obviously, healing spells would be significantly reduced in power. But now healer gear, such as class sets, help in all situations. There is no longer a divide between damage casters and healers, there are only casters. All of whom get the same rights as each other.
Honestly, I think that this would be a much better situation than what we have now. But it would probably be a lot of work to try to retune all the boss encounters to work with a reduced amount of +damage/heal. As unfortunate as it sounds, the best hope is to wait for the Burning Crusade expansion. In BC, Blizzard should phase out +heal as people reach level 70, much like they phased out +fire or +shadow. Then at level 70, all casters will be using +damage/heal, which will allow them to be effective in all areas of the game.