People usually concede when they've suffered severe setbacks and the opponent can just walk the ball straight into the end zone. Often, that means that a ball carrier has managed to get past the opponents line and out of range of any players trying to stop him. If the game were to continue, it would be a guaranteed touchdown.
Sometimes it's done because it means the conceder knows/thinks he can't win anymore, but it is also often done to deny the winner a vital level up, as a final FU to the opponent.
Getting conceded to does give you extra gold and an extra MVP, but random SPP going on a skink, skeleton or zombie doesn't compensate for getting it on the Saurus, Tomb Gaurdian or Flesh Golem that you've managed to pick up/hand off to.
Targeted SPP means a lot more than random SPP, but at the same time, a concede means that you lose the opportunity for future random SPP from various blocks and passes etc, so the extra MVP should not go away.
Therefore, I suggest that if the opponent concedes, the player currently holding the ball should get 3 SPP for a touchdown in addition to the current rewards handed out for a conceded game. Obviously, this should not apply if it's the conceding player that is holding the ball, only if it's in the hands of the winning team.