Simply laying new glass over the soft areas does not address the issue...the core has gone soft, not the outer layers (which den\pend on the core for stiffness). Typical way to repair a soft core area is to drill small holes through the outer layer of glass into the core but not through the ineer layer. Make a pattern of holes all across the soft area. Take a small syringer filled with epoxy thickened with light to medium density filler (get it near peanut butter thickness), then inject into the holes as completely as possible. After setting, sand off any lumps on the surface, paint or gelcoat the ares for appearance sake and you;re done.

This is only practical if the soft areas are limited in size. It does add weight, but not much on reasonable sized areas.