Yes, sometimes it's OK to say "I don't know". But sometimes it's really not. All people, smart or not, start off in a state of "I don't know". But if it's your job to know then you need to put in the work to make sure you know, or at least know as much as you can. Someone saying "I don't know" doesn't mean they are dumb or smart, it could just mean they are lazy.
On number 2 I just disagree with the definition of smart. A smart person knows when to listen to someone and when not. Should you ignore people with less experience? Of course not. Should you listen to everyone? Of course not!
Smart people definitely suffer from being human, like everyone else, and can become emotionally attached to their ideas etc. I don't think this is a "smart person" trait. But, even so, it is often a very good idea to not buckle to the pressure of fashion and short-term trends. For every story of someone refusing to adapt there is one of someone who was right all along but it took a while for the world to realise.