The title is fairly self-explanatory I suppose. I think these potions are pretty useful for just about every nature class (Druids, Sorcerers, Barbarians and Rangers who eschew armor), but can be difficult to reliably acquire in any great volume from scripted quests. I certainly seem to be expending them far more quickly than I'm acquiring them generally (if you're a druid using your animal companion, it can work out at maybe 4 potions per scripted quest). Having another source for them from Shuana would be quite neat.
Putting them at 8 resources, the same as invisibility potions currently are, seems about right.
This would be wonderful for gazers as well.
Underwaters too.
Actually, they probably should be set at about 3-4, rather than 8, given they cost much less that invis to brew.
They are at times far more useful than invis. The price is reasonable.