Even if there is less snow and more rain (I'm not getting into that part of the debate), is it enough to force ski areas to change their snow-making plans? Many areas make a set amount of snow and make that decision long before they know how much snow (or rain) they will get in a given year. The resorts I'm most familiar with have not made any substantial changes to the amount of snow they're putting down on trails. If there's a really bad year, they may re-fire up the system later than normal, but that's a one-off event that they don't plan for and isn't something that would be reflected as continually driving up costs (which was the start of this discussion).
Presumably resorts set their snowmaking budgets based on their own historic data. If their experience shows a decrease in snow or an increase in rain events, they adjust their snowmaking budgets as necessary to ensure that they can give their clients the sliding surface and season length they are accustomed to. I don't think they are doing this on the fly as weather changes.