I am going to say that chains will help you out a lot more than additional
ballast. The ballast can be a detriment for you when it is time to come back up the hill in the slippery stuff.
I would personally suggest the spacers. Reason being is that the front running gear is invariably weaker than the rear. By putting the chains only on the front you will be sending the lions share of the torque up front with little assistance from the rear.
It wasn't with chains but a friend down the road cleaned the splines off of his front driveshaft when he was getting bales out of a snowy lower field. The front tires caught traction and boom.
That is a different situation in that his tires were spinning and then caught a rut and got 100% traction but it is kind of the same principal and is something to consider.