I think that players playing in their best position and as starters have an advantage. I had very few players in all-star and not a starter despite being second best team in conference last season.
Worth informing about is that participation in all-star game has no advantages at all for the players. They get no improvements at all, neither in experience, form or in specific skills. That they played in an all-star game will only be available at standings for your conference so it will not increase player "fame" in any sense so that you can get a higher price when selling player.
All-star game is affecting your team as much as private leagues, that is nothing.
For some people all-star game is a fun thing though so hope you will enjoy it even if it is just for fun
