I think I'd only really paint something if I wanted to create a custom and felt comfortable that I wouldn't look back on it if it goes wrong and go what the heck did I just do! Speaking from experience outside of Playmobil working with mainly Action Man has given me experience in trial and error, most modern figures you can get ten a penny common as muck and ebay, there's not much variation in hair style and colour so repainting hair in another colour means more variety.
I find some colours like blond are harder than others to do and I find it hard to be neat so several coats and something with a fine point to scrape excess paint of is often necessary. I've also repainted an old metal car I've had since I was really small where the paint started peeling, dread to think how I'd cope with painting Playmobil as it's much smaller parts and besides there's so many figures with Playmobil there's not really the same need for me to customise to add variety.