Our fiberglass tub enclosures and hard water give us a similar problem to yours. I have used soap scum remover products for built up stains, but it doesn't spray on too well. Nonetheless that's still what I use when I clean. Once it's clean, I use a product that really keeps me happy: it's called GelGloss, which is basically a wax product that is for fiber glass. I NEVER use it on the floor cause it's too slippery, but on the walls, the water just beads up beautifully. (Someone else mentioned waxing the walls and this is essentially that) It's not cheap, and it's chemically smelly, so I don't like to use it often. The other half of my plan is our persistent practice of keeping a hand towel at the shower and wiping down the walls after every use. We both used to whine about the wipe up= hubby more than me, but it's well worth it in terms of cleaning hours. Good luck. (I used to get Gel Gloss at the hardware store - it's not in my Walmart- so now and then I pick it up at Lowes, since the hw store is gone.)