As I said, you leave behind the opportunity to fine tune the parameters.

Ok I see now the type of control you want on the spray tool : you're right, as it is an optional dialog, we can afford having many parameters.
http://wiki.inkscape.org/wiki/index.php/SpecSprayTool#UI

I just changed the tabs in a dropdown box, indeed, we don't know how many objects the tool will have to spray.
I added the "Master" item, the logic will be the following :
- if a checkbox for an object is checked, take this parameter
- otherwise look for the master : if the corresponding Master checkbox is checked, take these parameters
- otherwise, take the reference brush parameters as parameters.

Or maybe not ;) Scrap the radiuses. Ideally (again :)), I'd like to
set the density by editing a curve.
This is more intuitive and has an additional advantage: you can make a
painting cursor that has a hole in it. With the two radius approach we only
can set the circumferences, so having a hole or concentric rings is impossible.
If the user wants a gaussian distribution he could draw a gaussian curve,
(or use a default preset -yes, in my fantasy world curves can be saved;)).

Yes, the curve widget would be great. If you've used blender, you may be familiar with the power of such parameter control. (basicaly, the user can define curves between two variables)
In fact, the question is What do we mean when we talk about the "randomness"parameter ? If the user gives a curve, it's clear, but if we give a number, how can we define it ? That was what I tried to propose when I talked about distribution.

I think that a curve widget may be too complex to use (and to build). So considering the min and max value, this is what I propose as an internal way to convert the % of randomness to a distribution :
http://wiki.inkscape.org/wiki/index.php/Image:Random_spray.png

Steren