The mini-game itself should be fun, and in a game like this, it should only flavor the reward, not add or remove it. This is the ACIO playground after all, with supposedly few if anymore game ending endings.
Like take this scenario for example, Sarah challenges you to an optional dual in the VR game and the winner gets to demand something of the loser. If you win, you get a sexy scene where you are telling her what to do, and if you lose, then you get one where she is telling you what to do and is more aggressive in the scene. This way while you might want to do both to see both scenes, you don't really lose anything by only doing one or the other, or by not being good at it, or whatever. I mean, this could even be the same scenes, just with different dialogue flavor. If she wins, she could demand that you eat her out (maybe in the girl form? that could make it require different renders though unless the player was feeling adventurous the first time and wants to do it again) and if you win you can command her to lay down saying something like 'I want to taste you' as an example (to be nice it could also work into a 69 so they both have 'fun' lol).