Concur, why have the FMS Bridge Visual with waypoints in the FMS, and then basket case it to DME? If you dont have GPS, use the Quiet Bridge Visual.
The big reason is to provide an (automated) vertical path / guidance that the FMS can follow, even with older DME/DME based equipment.
At SFO especially -- with other aircraft flying "wingtip to wingtip" to you on a close parallel approach -- it's too easy for pilots busy maintaining visual with other traffic to either fly too low and bust minimums, or conversely stay too high and require high descent rates to get back on path.
With RVFP, the FMS can alleviate much of this workload and improve flight safety.
By the way, technically an RVFP is not considered a special instrument approach (visual approaches are not instrument approaches).