Depends on how many lineups you're making. In the end you probably care about diversity, not particularly uniqueness. Similarly to exposure, uniqueness creates really bad lineups if you're making a lot of lineups. For example: a player pool of 160 and a uniqueness of 8 (if max players per lineup is 8) will have a maximum of 20 lineups, and after the first few, the rest will be absolute trash. It is a very restrictive constraint, the more lineups you make the faster the quality of lineups decline.
I don't know the exact number, perhaps other users can chime in, but if you're making 100 lineups, I wouldn't go very high.