Reducing the clip_far to 2000 should increase the accuracy, right?
Ok, I see:
"camera.clip_near = 0;"
0 is an invalid value, because that would mean a divison by zero. Keep the value above 0 (or >= 1 as the manual suggests).
Theoretically yes,decreasing the clip_far and increasing the clip_near can increase the accuracy as stated by the manual. But I found that it works the opposite way, increasing the gap between them give me the better result, in fact, I'd just use the default value(by not setting any of them) for the best result.
For 3run's problem, there's a possibility that the sprite is zneared somehow, how about resetting znear flag each frame, just to see the result?
I've tried that bart_the_13th, but no way for it to be reseted. 
