It more hawks back to the early-mid gunpowder warfare era I reckon. Very early warships tended not to have much decoration because they were not typically all that big, though almost nothing is known of the really big Greek and Roman galleys which did not rely on ramming (ramming requires maximum possible speed, thus very low weight, to have any chance of ever ramming anything). Like 200AD-130AD though nobody was building big warships, and since wooden carvings get very heavy very quickly that rules out going crazy.
As far as anyone can tell, last I checked, were pretty sure the main reason people stopped decorating ships heavily in the mid ship of the line era was literally that the topweight became too much even for several thousand ton ships, they needed the mass for more cannons and more superstructure to hold said cannons. Cost was probably not the main factor though it was pretty high, even today making paint that withstands salt water is hard. For most of naval history command ships at least were heavily decorated, and it was considered undesirable to command a force without an impressive ship to inspire the men. In space topweight has no meaning....so its only a cost issue to hold you back.
This is a more or less accurate model of the Soleil Royal from 1670, its pretty epic, and it's still not as elaborate in proportion to the Vasa.
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As far as in universe goes, its all about propaganda, and at least for a space ship to be brightly colored and elaborate its not strictly speaking a clear disadvantage in combat (the mass would reduce acceleration, but it may also serve as some kind of armor). The Space Marines running around in bright colors and carrying tall banners meanwhile are actually putting themselves at a significant disadvantage.
"This cult of special forces is as sensible as to form a Royal Corps of Tree Climbers and say that no soldier who does not wear its green hat with a bunch of oak leaves stuck in it should be expected to climb a tree"
— Field Marshal William Slim 1956