Here is the example showing how limits+randomness work: http://wiki.inkscape.org/wiki/index.php/Image:Spray-tool-attributes01.png
I took my ideas and ideas from Steren. This hopefully resolves my issue with the concept of "randomness" which wasn't clear to me exactly how it should act (even when I was convinced that I wanted such parameter).
The mechanics for the rest of attributes (S, L and O) and dimensions (rotation and scale) is exactly the same.
Note that when randomness is set to 0, the value is always |(max-min)|/2 (it's an absolute value for cases where min>max).
I've to revamp a bit the toolbar for this tool, since with these changes some of the buttons can be scrapped (like scattering radius).
It lacks a way to select an original for spraying it. I thought about a button "pick original" in the main toolbar. When pressed the cursor changes to the normal arrow to click on an object/group and from then on that's the original (in clone mode all of the clones are linked to it, in the other two modes the object is just used for spraying but not linked to the sprayed items). Any (better) ideas?
Another issue: clones inherit attributes so is not possible to set these parameters. Un less there is a way to make clones where the only feature inherited is the shape.
Regards.