I've cleaned up after a clumsy plasterer quite a few times. If it's still wet it's easy, when dried takes more time.
Chemicals/machines are of lesser importance, all you need to be able to do is rinse it really really well... if dried then AFTER you do the important bit - you have to break up the plaster first!
The way I've done it in the past is with a handi-groomer, stiff brush and even a flat screwdriver down the gulley of the carpet next to the skirting. You just have to agitate agitate when the plaster is dry, to break it up. A good cylinder vacuum is essential to suck up the dust as you go.
After you've got no more loose debris there that you can agitate and vac away, then is the time to soak it really well, agitate and finally rinse like hell. I'd only ever use a hand tool or stair tool on a bit bigger area, because you need to recover all that water very efficiently.
Saying that I've never done a plaster spill with my new TM yet so don't know how much easier that would make it!
Polyprop should be as good as 100% results, wool varies according to different factors