Any kind of programming can become just as addicitive as 3D modeling . . . I like programming in MEL because I can do both the programming and build the models, so I am not doing the same thing all the time . . . but for someone who does not really understand programming, they may find it hard to see how it can have much appeal.
Building a raytracer is definately a good exercise, even if it is re-inventing the wheel . . . . and who knows, after you have re-invented the wheel, you may come up with a new feature that no-one has thought of yet, to add to the wheel . . . .
"The Sage as an Astronomer: If you still see the stars as something above you, you lack the eye of knowledge." Friedrich Nietzsche