Why should parking cost a whole lot more in the future? This system is being managed with the goal of ~85% occupancy - if there is less than that, prices will be lowered, eventually to $0, to seek optimal occupancy at all times.

The only way that parking would, in general, cost a whole lot more in the future was if there was a whole lot more demand - and I'm not sure anyone is predicting that we are facing an imminent increase in the number of cars seeking to park in San Francisco.