I'm not sure if scents make a difference...my limited experience hasn't given me anything, either way. I DO have some oil that I add to a mix, whenever I think I should. I use VooDoo brand Cold-Pressed Menhaden Oil. It's cheap. It's real. It mixes into plastic very nicely. I've taken a soft plastic that had the Oil in it, and set it on a piece of paper. When I pick it up You can see where that bait laid...it leaves a slight spot of oil on the paper.
I'm not sure if the oil can/will make any difference in influencing a fish to open it's mouth, but I'll be "researching" it for awhile, and will be sure to post any findings, here. One thing the Menhaden Oil DOES do, is soften the plastic. I use CCM Hard, and 1 TSP in 10-12 oz.s of plastic makes quite a difference in the stiffness of a bait. I believe this will be most of my "softener" 'til I find a reason to get actual softener...even then, it better be a good reason!