What about adding tree saplings as a crop? Most of the vanilla trees would be purely decorative (such as birch and jungle trees) with a small chance of dropping saplings if harvested when fully grown. Oak trees could drop apples at a low rate as well, but that's not really the point of this suggestion.
The point is, what about adding new trees, available only through IC2 agriculture cross-breeding? I can't think of any at the moment, but new wood colors, higher wood yield, or other desirable attributes would be cool.