In a 2006 Prius, are the steering wheel buttons well lit or dim? I find them to be dim and hard to see at night.

Yes they are dim and not adjustable by you.

Steering wheel buttons are lit in the courtesy light fashion, they are not well lit or bright like dash lights, but they are lit so they don't just disappear in a dark cabin. All of the wheel buttons have bumps, dimples and lines. After a while you should become naturally familiar with their location by using the bumps, dimples and lines to fell your way around. When you become that familiar with the vehicle, then you will no longer feel the need for them to be illuminated.

It has been said:
Hybrid drivers come in 3 flavors, greenie, techie and cheapie. Pick any 2.
2005 Prius, Melinium Silver over gray, package 5 (AI)

I know the bumps on mine and still want them with better lighting. Toyota should have allowed us to be able to adjust it.