Hi Robert,
Fine sanding a kayak hull to improve its performance is a good way to build up muscles in your arms which might make you a 'stronger' paddler but any effect on waterflow on the hull is neglible at the speeds we move at.
Deliberate non-smooth surfaces have been experimented with for decades, copies of the shape of shark's skin for example. They work but usually for a specific speed range. Outside of that range, the effect is at best neutral, more usually there's some drag penalty.

Just as interesting was an experimental 'soft-skin' oil transport system. Basically a large sausage shaped bag filled with liquid (fresh water for the tests) that was towed by an ocean tug rather than building actual oil tankers. Using a comparable volume as the base for drag, they found that the bag had a much lower drag as it deformed, coke-bottle-shape effect, for minimum drag at its entire speed range.

Mike Savage
South West Cork