How do I fix these paint cracks? Should I do it myself or go to a body shop?

 

It doesn't look that bad. I'd leave it alone.

People can usually tell a DIY paint job from a professional one.

The sun has faded your color with 14 years of UV , so it's no longer a factory match.

Shops can mix paint and spray it. You're stuck with what you can buy in cans.

 

Yeah I would leave that alone, the poly is pretty deformed from bashing into stuff anyways so you would be repainting a bent piece of plastic.

To make it less noticeable you can go down to Nissan and pick up a paint pen of touch up paint and just lightly hit the center of the cracks.