Maybe for the story with it being too simple and black & White is because Cameron wrote it back in 1994 and he just left it to wait for the technology to catch up. Seriously i think he should've done some rewrites.
And you know, after watching the first two Indy movies again, I'd like to change my vote. I mean, I know Willie is annoying 'n all, but I think she's pretty hot. I really don't like Marion, with her cursing and ability to drink so much. She'd be an expensive date, and that's just too manly for me. Willie is a hot, dumb princess with big norkers.. lol. And she is sexy as hell at the Indian dinner table scene.
I can see someone like Lucas doing that, Writing a brand new story and then leaving it waiting for better special effects and then just doing it couple years later.