Is a gravel jersey worth the extra cost over a basic road jersey?

For regular gravel riding, yes. The durable fabric alone justifies the premium — a road jersey that gets shredded on thornbushes is a false economy. The extra pockets eliminate the need for a frame bag or backpack on many rides, and the zippered security pocket prevents the expensive mistake of losing your phone on a bumpy descent. If you only ride gravel occasionally, a road endurance jersey can serve double duty adequately.