I think Todd's big reasoning for leaving fans out of some games is that they are noisy and bring more dirt inside the cabinet, and some cabinets have fans regardless of whether the particular hardware inside runs hot or not. Personally when I get a cabinet with a factory fan option installed, I typically leave it in but will usually replace any AC powered fan with a 12v DC fan. They run much quieter, are more efficient and generally suck in less dirt.
With all that said, I never knew Galaxian cocktails had a fan. I have an upright, no fan. And I've seen several Pac-Man cocktails (very similar hardware), none of which had fans. I don't see why you'd need one for your game, but if it has one it certainly wouldn't hurt to clean or replace it.