p/w's are still welcome in most parties... they just want our 10k heals and don't want us to dps.
Heck, yeah! You are P/, so let's see some heals and not have any of those "but I am not really a priest, I am a battlemonk" talk. :p
As for the original subject I'd go with healers.
Many instances can be run tankless if you group is OP enough so that the role of meatshield is needed that much less. And if your DPS/healer cant take the AOEs, there is only so much you can do as a tank to protect them.
DPSes are needed, of course, but they are interchangeable. In most runs, you have one tank, one healer and a bunch of DPS. So, unless you are seriously OP, your demand will be not for you, but "one more DPS".
Healers, OTOH, are life of the fight. If the healer can't keep the tank or the DPS up, the risk of wipe goes up tremendously. Maybe in scout burn era you could go with so-so heals and try to DPS the boss in just a few seconds. Now with burns being harder, the ability of healer to keep everyone up is more crucial.