Wouldn't flash washed out most of the text? However, if you find that good enough for you I don't think you should worry about the flash life.
Like all electronic gadgets any part can eventually give up the ghost first. For the case of the camera that can be the sensor, the shutter, battery or the flash that will die first. I don't think any camera will die because you take 200-300 images in one day. If you are worry you can always give it a break in between when it gets very hot.
The in-built flash is designed to last the lifetime of the camera.
Nikon D90, D80
Nikkor 16-85mm AF-S DX F/3.5-5.6G ED VR, Tamron SP AF 28-75mm F/2.8 XR Di LD Aspherical (IF) macro, Nikkor 50mm F/1.4D, Nikkor 50mm F/1.8D, Nikkor AF-S VR 70-300mm F/4.5-5.6G IF-ED, Sigma 105mm F/2.8 EX DG Macro ||| 2x SB800 | SB600 ||| Manfrotto 190XB