I think filling the tires would be a nice option. I think it would help turning when the terrain is hilly. I have a new 757 JD and it handles hills well, but last week when mowing for my neighbor, I hit a wet hill that sent me skating. I had no business on the grade I was on, but it came upon me before I fully knew. I started "skating" and that is scary. It seemed no matter what I did the mower went faster. I would have only hit an electric fence (ouch) but still it was not fun. I think having loaded tires would have allowed me to steer out of the problem a little easier than I did, but I still got out of it without dying. I would do it. Anti-freeze or methanol or an environmentally-friendly doggie friendly RimGuard would not cost that much and you could always take it out if you did not like it.
John M