I've had to start using some of the newer "Liberties" along with my older Mixos and haven't seen a difference.
Years ago, the fact that Mixopake was the only Pantone approved opaque system meant more when we printed a lot of P-F-P, rather than underbasing.
I use my system now almost always adding some base to increase its WOW abilities and make it more like Ultrasoft.
Sounds like for you, it may still be the way to go.
For me, mixing a lot of small quantities, I found the pigment based systems too difficult to work with.