The bolt in sprags aren't any stronger than the unit in the vehicle, they are just easier to change. Not worth the effort if yours isn't messed up.
I have rebuilt several trans. but am no guru but I thought the reason for going with the bolt in sprag is it resists spinning in the case better. You are correct though about if it ain't broke don't fix it.
I think Turbo Action makes a full manual valve body with low band apply.