If you have any rough spots (or dull areas!) from rubbing printing off (I can see this being quite an issue on something like red plastic) try some 'rubbing compound'. You can get it in several 'grits'. 3M makes some good automotive industry products. Just use the telephone book and look under 'autobody supplies' and call a few shops. You probably don't know them because they will be specialty shops but once you go in you will see a plethora of useful stuff!!!
Wet sanding is also a good option - ie 2000 grit paper.
I would recommend getting a Dremel type tool. You can get knock-offs for half the price that work just as well - Sears, HomeDepot, etc will carry them. You can get a polishing pad and put the rubbing compound on there and use that to polish a LOT faster than you could ever do by hand. You should be able to get an attachment that will hold velcro backed sandpaper - this is how you polish with the wet/dry sandpaper.
Actually, just get one for your regular drill. Playmobil is large enough and the bigger the sandpaper/polishing disc, the faster the job.
