Definitely a good idea.
A racing line on an aerial view would be good. So long as it has a consistent style between all tracks it'll look good. I'd suggest doing sections along the following lines:
1) General description of the track
- Short / long
- Run off - lots / little / gravel
- Any areas that are important to get right for laptimes
2) Turn by turn description
- Turn name / number
- Screenshot (with racing line?)
- Description of entry, exit, braking, acceleration points
- Any features - gravel trap, don't cut, nasty bumps
3) Lap Description
- How to string the corners together, how to tackle complexes, in depth discussion of the important sections
The above may repeat a little of the information, but it'll be interesting to read, and use as a reference.
To do each track for each car would be hard - you'd need to have section 4 and have a table for braking/accelerating points for each car and turn. Possibly not worth the effort - that's something that each racer will decide for themselves.
Finally, for further insipration, see the BMW track guide for the nurburgring.