The spreader gradually losing all its weight would not spin as well due to the load lessening in the hopper.
Filling the spreader tires with windshield washer fluid would help some with the above issue.
To maintain traction you would want to have more tongue weight by adding a solid cinderblock to a beefed up frame. Putting the block on top will only make it top heavy and it will tip over and bend the tongue of the hitch.
You would have to make a new tongue/frame for the spreader to hold the weight as the tubular steel they use will not hold up.