Vaughn-Tom Selleck, Kent McCord, Chad Everett
My pick: Selleck. He has the rugged thing, plus the twinkle in his eye that I imagine Vaughn has. Plus, I think Selleck could pull off a more world weary role as well, after he played Eisenhower.
Shar-Rainbow Sun Francks
Francks is slender, has an openness, and I think he can pull off the alieness of Shar. I think CCH Pounder would be excellent for Shar's mother.
Bowers-Derek Luke, Anthony Montgomery
Either one of these guys. Both are young and have muscular builds. I think Luke is the better actor, but I would like to see Montgomery get some screen time, and an important role, on a Trek show.
Taran'atar-Phil Morris, Tony Todd, Christopher Judge, Keith Hamilton Cobb.
All of these guys could pull it off. But I think Morris and Todd could do the more settled, wise and wearied warrior better than the other two.
Prynn-Linda Park, Ming-Na, Kelly Hu
Leaning towards Linda Park because I would like to see her get more time in another Trek role as well. Plus, I think she can pull off Prynn's rebellious, fun, and sexy sides.