Finned vs smooth brake drum

Improvement? Yes. Noticeable improvement? Maybe. Big improvement? Even at peak efficiency, 9" drum brakes are limited as to their effectiveness versus larger drums and discs. Brakes convert kinetic energy into heat, so any way to better dissipate the heat will improve their function. Fins increase the surface area from which the heat can be released, providing better cooling.
If you can find them, try them. As long as you have the brakes apart, consider changing the shoes to those with an aggressive lining material.
Enjoy your scenic driving! I looked at a satellite view of Andalucia and along with mountains, saw olive groves that seem to go on forever.