Most of the time, the key is to remember that, by using an infusion, you are essentially creating a temporary magic item. Bull's Strength's Target line is still the creature, but you affect the creature not by directly casting on it, but rather by enhancing a belt or gloves or the like.

Natural Weapon Augmentation could be thought of the same way. There are magic items that modify natural weapons, like the Amulet of Mighty Fists and the Necklace of Natural Attacks. You're temporarily turning some item on the creature's person into one of those, basically.

For Walls and the like, it's trickier. One option might be to think of yourself as turning the room into a temporary magic item, like the Wondrous Architecture from Stronghold Builder's Guidebook.