1 and 4.
I've changed nut/saddle on around 20 acoustics - all improved volume and sustain. When tone is too bright I prefer to dampen it with ebony saddle. I use heavy guage strings which also mellows tone. I guess option 4 is a reality because there is no reason to change nut or saddle when they are already bone or ivory and in good shape etc. Most consumer priced accoustics come new with plastic components. That is when option 1 is the deal.