There's no Planar Renovation project for Arborea (and it probably doesn't need one), but I thought of roles for both the Eladrin and the Bacchae.
For the Eladrin, I envision one of their primary roles against the fiendish races is rescuing of mortal blood war conscripts, including the removal of Fiendish Brands from those who took them under coercion. This of course would take the form of subterfuge rather than actual warfare, of course.
For the Bacchae, I thought a good role would be rescuing mortals ensnared by the Grey Waste's power-- essentially kidnapping them and taking them back to a gate town, or something. For the Bacchae and Dionysus, the greatest tragedy of all would be the loss of ability to experience emotion or pleasure. In addition to rescuing them, the Bacchae (or the Dionysian priesthood, or a guild of the Sensates, or both) would likely put the rescued victims through some sort of rehabilitation, perhaps reintroducing the victims to color and sensation slowly so as not to overwhelm them or drive them to insanity (I haven't read the Grey Waste stuff from Planes of Conflict for awhile, so I don't remember what happens if the victim is forcibly removed from the plane). The question of course is how the Bacchae could do this without themselves becoming victim to the plane. Perhaps their passions are so strong that it simply takes longer than usual for the Grey Waste to have its maximum effect on them...
Both celestial races would likely focus primarily on rescuing non-evil victims (or at least give them first priority).
I already had the eladrin filling such a role in my campaign (along with sabotage). But that is a good use for the Bacchae who always just seemed like a bunch of abnoxious frat boys. Since they are agents of a good plane, they should have some purpose towards helping good (at least on occasion)