But I suspect I may settle on the pilot hole-pan head screw approach. The reason being that it may be the best way to keep pieces lined up. Even with spacers, wood can put put up a struggle.

No doubt that's why they use this method on these decks(although I'm not sure they did 15 years ago-they do now). They have more challenging compound curves to deal with. I think the plugs look fine, and knowing they're solid makes me comfortable.

The low light last night reveals the extent of 15 years of washing, sun, rain, foot traffic. Age gives the teak more texture as softer fibers wear away first. And you can see the teak is fairly moist/expanded at this point as the caulking is proud of the teak. No wonder this is a near perfect 'footing' surface on a wet moving sailboat deck(excluding $).