I'm a bit of a noob to blender, but for Bezier curve point radii, how can I assign a specific value to all selected points, vs the unintuitive "Mean Radius"? E.g., I don't want to preserve the proportions - I just want all points to have a radius of 1.
You can control curve radius proportionally with Alt+S or the Curve Shrink Flatten operator as you already know. This will proportionally scale all vertex.
So set an absolute value for all selected vertex use the operator Set Curve Radius either from the tool shelf, or the space bar search menu, and enter the desired value.