I have two Dremels, one with no speed control other than on/off; the other is a 4000 with variable speeds down to 5000. I don't either obviously for the models.
Today at the BX, I was lookin around for things to use with the models when I went down the aisle for finger nails etc ( my daughter does this stuff) and I noticed a AA powered hand tool for grinding/ polishing/sanding of nails, for only $5. Just tried it out when I got home and it works pretty good IMO. Real low speed. Even has a kit with 5 bits.
I figure its gotta be 'gentle' on fingers nails so why not work on styrene plastic too.