The only sure way I know to get more colour saturation and sparkle in a colour print is a method I used quite a few times many years ago. However this is not over exposure of a negative as requested by the OP.
(there was a url link here which no longer exists)
If that link works, it will take you to my gallery, there you will find a half colour and half black and white print.
The explanation is in the text.
I think most of you are forgetting the original person and his request.
He is, as far as I can work out, not using electronic means for obtaining colour saturation. He is not wishing to use electronic means.
I don't use electronic means, I just fiddle with things and if I wish to know something I'll research as far as I can, then I'll do my own experiments to ascertain if what I have gleaned works for me, or is true.
PE, very interesting. I remember reading somewhere else on this forum about your experiments regarding over exposure of C41 colour negative material, as you have just re-explained.
Mick.