Considering replacing blown cellulose on attic floor with open cell spray foam. Should I just leave well enough alone?
Not crazy but quite unnecessary and counterproductive.

Unless you are visiting your attic often there is no way for the cellulose to get into the living area of the house. Much less the cellulose in the walls since it is sealed behind the walls.

I suspect most of your dust comes from other sources.

You said adding ventilation has eliminated your moisture problem. Don't worry about it then.

So, I think you are contemplating spending a whole lot of money for much less insulation R-rating. Then you will also pay more for heating and cooling from that day forward.

It would be much cheaper to hire a maid service to come clean your house once a week.

Good luck.