I wouldn't soak them overnight. I think that saturates them with plain water that has to be displaced later with salt water. A half hour soak is enough to soften the shell and start the process, but the soak isn't really required. Use plenty of salt. One cup per gallon. Any seasoning has to be pretty heavy to permeate the peanuts. Shrimp/crab boil is an option. Ham hocks is another.
I've never found the process much sensitive to issues of how long the peanuts have been stored after harvest. Plain old raw peanuts in the bag from the grocery have always worked. So I suspect timid seasoning, because if they cook until soft, they're getting the seasoning.
"Kitchen duty is awarded only to those of manifest excellence..." - The Master, Dogen