Wow, speedy response: thanks Remus. I'll see if Grow does the trick
FWIW Jim's Mover2 is nearly what I need, except it doesn't do multiple iterations, or scales as the name implies. Pretty good apart from the sticky 'copy' toggle which needs to be a radio button I think.
http://sketchuptips.blogspot.com/2007/08/plugin-mover-2.html