Im no historian

but I think there something else to be considered when thinking about armor

I would image armor would be handed down through generations - particularly in a militaristic society - I would envisage the eldest son being given the armor of the father who inheritied it from his father

it would be like a prized family heirloom, kept polished and stored in oil skins

so I think it is possible that any particular soldier could posses fairly elaborate armor be it somewhat antique

so when faced with the choice of armor styling it would be reasonable to err to older or antique armor over perhaps later models for this reason

also given the pride the spartans took in their physical appearance - I think it would also be reasonable to assume that some artistry wouldve gone into their families armor - simplicity in design but done beautifully - I would imagine.

and as there is little hard evidence - I think there is some room for artistic licence here - we shouldnt fall into the trap of making them resemble peasants because we thought them to live in primitive times - some of the most primitive people have the most elaborate, colourful and beautiful ceremonial dress - look at the tribes of PNG