Maybe you can use it for hotels?
Most hotels make a copy of your passport nowadays.
I did use the W.S. PP for 3rd world hotels where the clerks were illiterate & blindly made photocopies of anything that looked like a passport.
The other reason I used a World Service passport was that in some places in Africa, the passports were just stuck in pigeonholes overnight where the room keys were also kept. The desks were often left unattended and I was worried that my real passport might be stolen. If this happened in some obscure little country with no embassies or consulates I would have been screwed. So for me, the WS passport did have limited use. Now that I am an 86-year-old codger, I am not so adventurous. I stay in big towns of major countries; in minimum of 3-star hotels. In Europe for instance, they don't just leave passports out for anyone to take. So I let my old WSPP lapse because I don't need to use it anymore.
That leads me to another anecdotal story. Not so long ago, I needed to get a visa to India in my passport. After filling out long forms with incredible questions like "Did your grandparents ever visit the areas now known as Pakistan or Bangladesh? " Huh? I didn't even know the names of my grandparents, much less their travel itineraries of 150 years ago. So I just answered "No." It took weeks for the Indian Consulate to process my visa app. Pretty funny as I wasn't even planning to get off the boat in India. Yet, I needed this according to India, for being in "Indian waters on a cruise ship without disembarking."
Crazy huh? But here comes the worst part. I go to pick up my visa at the Indian Consulate in Europe and there are maybe 250 people, mostly Indians in the waiting room. The Consulate employee dumps maybe 250 passports on a table. We are told to find our passports in the mess. Anybody with a lousy passport could have made off with mine. Fortunately, that didn't happen, but after that experience, I decided to never take another cruise that passed through "Indian Waters." I didn't mention that this visa cost a lot of money. And when my Costa Cruise got into Indian waters, all passengers were FORCED to get off the ship, and stand (hard for an old geezer like me!) outdoors with no shade or place to sit in the 37o hot sun for half an hour, while our passports were inspected by 4 different immigration officers for proper visas, etc. I had visited India before, but after that experience, I said, never again!