I would think a major consideration would be the utility of deck plans, as in how often will a playing group actually make use of them. Deck plans/floor plans are usually needed for combat or more rarely if one needs to know distances like is character A close enough for guest alien B to use Telepathy (or something like that). I have deck plans of ships from a similar FASA rpg and only used them total of four times during a campaign, twice for boarding action combats in a several year campaign. But that was that game. If Traveller Prime Directive will be doing a lot of onboard combat, please include them. If not much, great eye candy, but don't worry about it. It's the same with Third Imperium setting deck plans. Having the deck plans for a Tigris class dreadnought are cool to have and look at, but the setting lends itself to have combats occur more often on smaller ships like the Far Trader/Fat Traders and the ubiquitous Type S Scout for more players.