Workshop

The first point is often found in role-playing mafia games. And it works quite well (if the players are willing to role-play in addition to playing the game), but it is difficult for the GM (because calculating the balance under such conditions is a nightmare).

The GM at his discretion can give small bonuses for good role-playing.

This is a bad idea; you don't even need to try it.
“At his discretion” can be replaced with “the bonus is given to the one who completes the task that the host assigned.” The bonus is usually agreed upon in advance, and there are many other rules. In general, it is an interesting but complicated practice. You need to get used to it.