vellum hair thickness

To randomise vellum hair thickness, you use pscale values. To get Vellum to recognise these values, UNTICK the Thickness box in the Vellum Constraints node.

polywire radius

To vary the thickness of your polywires, simply type in the @variable you've made into the "wire radius" field of  the polywire node.. A rather simple thing that I should have figured out *facepalm*.

spinning particles/points/rbds

I made a previous post about spinning particles with "w" and Pop Torque.... Walter uses this & it seems much simpler (?). In your DOP network, create a Pop Spin node & in the VEXpression space type:

spinspeed = 100*(fit01(rand(@id),chf("min"),chf("max")));
axis = sample_direction_uniform(rand(@id));

Spinspeed is measured in degrees per second
Axis specifies the axis of each point you're spinning. The sample_direction_uniform() function returns a normalised vector. So here, we have a completely randomised rotation axis. Not bad.