Will this scrape on steep inclines or driveways?

The diffuser mounts directly to your existing rear bumper, so clearance depends on your bumper's height. Check your current ground clearance at your steepest approach angle, then measure from there to your bumper's bottom edge. If you're already bottoming out, this adds minimal risk. If you have good clearance now, you'll maintain it.

Does the grid pattern affect airflow, or is this purely cosmetic?

The grid design is functional—the open pattern allows air to pass through without creating turbulence at the rear axle. It's not a full aerodynamic wing, but it works within the diffuser's natural air direction rather than blocking it.

How do I maintain the clear coat finish?

Wash regularly with mild soap and water, then dry with a soft cloth. Avoid automated brushes and harsh chemicals. If the clear coat gets scratched, you can wet-sand the affected area and reapply clear coat to maintain UV protection—sand and prep the surface before applying your chosen finish.