I haven't tried it, but has anyone negotiated with a host over free play?

Yes, I've asked for additional free play to see if the host could "update" my existing offer, but I never actually negotiated to say I wouldn't make the trip without getting something extra.

I would think that "negotiating" free play would be something only high rollers could do who could also say to a host "I am going to gamble XXXX amount for XXXX hours." I don't do that -- and frankly I can't since I have a limited budget.

On my last several trips when free play was offered I've asked for additional free play but was told "no" but still made the trip.

For New Year's there won't be any free play and I never asked for any. I also wouldn't expect any.