When I first heard about General Grevious, I thought that's exactly what the character was going to be. To sort of tie the first and third episodes together and to fore shadow the Anakin/Vader character.
I thought the exact same thing, really. If it can be pulled off professionally, I think its a good idea, but nothing should suffer too much because of it (like the pacing/flow of a scene, or a good piece of music etc.).