I have been pondering back and forth again on mineral wool. As far as sound deadening, I think cellulose is close. They are both fantastic though. My house has 15" rock wool and one of the most frequent comments we get is how quiet it is.
They benefits of passive house are way more than just saving money on heating. My biggest observation living with this house has been peace of mind.
One morning was about -40 and the propane didn't want to flow. The house was still cozy and warm, so I just left it and didn't worry and soon the sun hit the tank and the problem fixed itself. A normal older house you would be pretty panicked to get the heat back on.
Another thing is the price of energy. So the price of propane goes to $20 a gallon. We can still work with that. In fact I advocate the price of energy should be higher. After all, people won't conserve something that is cheap.
Comfort is another thing. It's pretty hard to explain, but a house with no drafts, nice humidity and fresh air via an HRV is way more comfortable than one that is just warm from a furnace working over time.
So quiet, comfortable, and ready for any disaster are the 3 reasons to build a passive house that I preach to most people. Most people that build new houses don't really care about saving on energy bills in my experience.