What happens is this: Once the clear coat is cut through and into the color, it will recover and shine when polished, but the shine doesn't last very long anymore.
Not throwing cold water on your effort. Short of a paint job, you did the next best thing. It's old paint and you shined it up. It is what it is - either polish it or drive it around skanky looking.
Just keep a coat of wax on it or glaze and it'll do fine.
That buffer/polisher is very nice looking. Certainly one a less experienced user could have success with.