my original reasons for selecting the show ship method were fairly simple. i liked to mont gatling guns forward of the cockpit so you could see them spin about when firing. to give the impression that your flying a machine instead of just a camera floating around in space. then i wrote scripts for control animations, so you could watch the cockpit controls move in reaction to your inputs. this involved a subsystem handle which is not available in the cockpit models which were implemented later on. i argued against the deprecation of the show ship flag for this reason. then i developed rtt code which required some texture replacement, and at the time there were no texture handles for cockpit models. i believe these limitations have been overcome since then, in one way or another. you can also now render objects on top of the cockpit model, this allows better animation (like translations) inside the cockpit. switching over to the "more efficient" method is now plausible and desirable and will probibly be done when i find the mood for modding.
detail boxes in this case, i think, is kind of a misuse of the feature. a low poly cockpit can have lods, and these lods can be adjusted to best align with the ship model at each detail levels.