OK. I can verify that the Malossi Kevlar belt sized 795-19.8-30 is a direct replacement for the factory belt in the People 150. Also, the Dr Pulley variator for the GY6 150 works well. With 13 gm sliders installed, I could notice a seat-of-the-pants improvement in take-off acceleration, but lost a couple mph maximum speed. I put in a set of 15 gm sliders and I would say acceleration was similar to stock and that, in combination with the Malossi belt, I might have picked up 3-4 mph top end.
I would say that, so far, the performance gains over stock vs. time and money spent achieving them are not worth the money. I think the 50cc scooters can be changed dramatically with modding, but the People 150 performance is apparently nearly optimized at the factory, at least with the stock carburetor. Whether a larger intake manifold and a couple mm larger carb would change much is a question I don't think I'll bother to investigate. And the CVT drive ratios with the 16" wheels don't allow sustained top speeds even on mild hills at WOT.