So my point is not to fill some quota or to increase replay value - it's that a good variety of companions is required to give players choice. If I have 6 companions to choose from, chances are that either I as a player will like none of them or it will be jarring for my character to hang out with those particular characters. No amount of "depth" (or crammed content of whatever quality) will matter if I can't have a party I actually like. Hence my opinion (as kanisatha's) that 12 "full" companions is a minimum. This is what WotR has now and from what I understand, they don't seem lacking in writing, content or reactivity. The additional 12 I mentioned is as a low-cost bonus to further expand on choice.
Planescape Torment had only 7 companions and it worked really well. BG2 companions were... Well, they had nice writing, but most of them felt pretty generic. Not in a bad way, mind you, and not all of them, there were several standouts, but the majority of them were your average high fantasy adventurers with basic backstory and basic personality.
