There is a way you can play as the Nintendo All-Star team but only in a 2-player exhibition match. Here's how:
Go to Tournament mode and select CONTINUE. Enter the following code to open the expert mode:
Up-right / down-left / right / down / down-right / left / down-left / up-left
Now you'll be taken back to the title screen where you'll see the word EXPERT appear underneath the title. Now go to TOURNAMENT and start a NEW GAME to begin expert mode.
There is one easy way to score in Super Soccer - and I mean seriously EASY! It's easiest to do this when shooting 'up' the pitch (i.e. you can see the goal from far away). Basically whenever you get the ball in the opponent's half of the field, line your player up with the edge of the goal, aim straight forward and shoot as hard as you can. Even if you are miles away from the goal you stand a chance of it going in but if you are 20-35 yards away it's almost certain to go in the top corner - as long as you lined it up right.
It only takes a few attempts to get the hang of this and start rattling up huge scores. The only trouble is it very rarely works against the real good teams like Germany and Italy - and never works against Ireland because their goalie is just too good.
Also, another quick tip for scoring: Aim diagonal shots just inside the near post (specially the bottom corner)!