[Pault]

Think about it this way: if you don't power the outside wheels, they will spin freely. So when someone pushes you from the front, they won't resist, they will just spin. However when somebody pushes you from the side, they will resist in the same way that a power wheel would. However, this also means that you will have more trouble turning, because when you turn the force is perpendicular to your wheels, resulting in the same effect of having it not matter if the wheels aren't driven. On the other hand, if your robot is light and you don't weigh it down, that will hurt your pushing power in all directions significantly and increase your turning ability.

It's up to you to decide how this info will affect your decision.