My thought on this is that if the rim looks perfect (no substantial scratches, dents, and the rim is 100% true and did not have to be bent back into original shape) then what might have happened is that only the spokes and or the hub was damaged. Metals have a specific amount of springiness. Up to a certain point a metal will flex under load and then return to its original shape once the load is removed without a change in the materials properties. Once you exceed this maximum point of springiness the material deforms and even if you are able to bend it back to its original shape it will have lost strength.
Is the rim true in all dimensions? It might lay flat on a table but is not necessarily true. From the side view is it a perfect circle? If the impact came not from the side but from a taller angle then it would lay flat but might be other than circle (egg shaped or a circle with a flatter spot on the outer diameter of the rim). Also what might have happened to your rim is the same thing that happens when you over tighten spokes which is the spoke nipples begin to stretch the material around the hole where the spoke nipple nests deforming and weakening metal around nipple hole which increase the chance that the whole nipple could ultimately just tear trough the inside of the rim. This could have occurred in your case from an impact to the spokes. In might have stretched the spoke nipple holes out which would cause the wheel to not spin true because the relative tension of the various spokes changed because of a permanent change in the shape of the wheel.
As for the spokes I would throw any away that show signs of impact or having been bent beyond the point of springiness even if they are steel. What you keep depends how careful you want to be. If you have several compromised spokes then a hard bump could lead a massive failure of several spokes causing your wheel to taco causing you do go down dangerously. But even one spoke breaking can be dangerous. I have seen a loose spoke wrap around the hub which caused the wheel to lock up which can be just as bad.