While the Splats and the like *CAN* be used in a 3.5 game, moderation is called for.
It's pretty apparent to me that the 3.5 Animal Growth was *meant* to be able to be cast on the Druid. It's also pretty obvious that Nature's Avatar and Nature's Favor and the like were not supposed to be cast on the Druid, unless they are shapechanged.
Hmmm...Shapechange. That kinda messes with my argument, doesn't it?
Realizing this, the developers of the spells in 3.0 must have realized that the spells could be cast on the Druid in question using Shapechange. I have no problems with Nature's Avatar, as the Druid would get that the same level that she would normally get Shapechange. Nature's Favor, however, can be gotten a lot sooner, and I am hesitant to grant that ability at a low level.
If I were DM, and my players told me that he was planning on using these spells (I don't allow stuff in other books unless the players run them by me first), I would actually allow Nature's Avatar, but not Nature's Favor.