StreamOfTheSky
Adventurer
The spell description for Wall of Fire just says "the wall deals 2d6 points of fire damage +1 point of fire damage per caster level (maximum +20) to any creature passing through it." If you pass through three times, I think you would take damage three times.
If you passed through it once, you've passed through the wall and take 2d6 +1/CL damage. If you passed through it 8 times, you've passed through the wall and take 2d6 +1/CL damage. I understand the logic you're trying to apply, but couldn't I also say, "Nowhere does it say I take 16d6 +8/CL damage! I passed through it, I take 2d6 +1/CL, as the text explains."
Ultimately, it comes down to common sense and game balance, especially the former. Yes, the rules often defy common sense, but that doesn't mean it should be tossed aside when it's a viable explanation.