Should I actively circulate air into conditioned attic?
Here’s an interesting article on this subject by Joe Lstiburek of Building Sciences.  In short, he says there has to be air circulation between the house and the attic in order to remove moisture from the attic.  In older installations, leaky ducting in the attic provided enough circulation.  In newer installations, ducting is often so well sealed that moisture is not removed from the attic and can lead to problems.  

His recommended solution is to provide HVAC inlets and outlets in the attic which provide about 50 sfm per 1000 square feet, which is about 1/3 to 1/2 air changes per hour.  However, there is a conflict with current building codes because spray foam is combustible and the codes do not allow vents in an attic with exposed foam insulation.  His recommendation is to change the building code to allow this practice, as long as a smoke detector is installed in the return air duct.  His article says 2018 is the earliest that change could be made - I don’t know where it stands.

I think the conclusion is that if your ducting is a little bit leaky you’ll be fine, but if it’s really well sealed it gets very complicated.