Yeah make them so expensive that only people like you who have nothing else to do but play the game can afford the time to get credits to buy it. Love players who want to keep certain items only to themselves.
No make housing and customizing accessible to everyone.
No, just expensive enough that it becomes an end-game market - because we really need something to do at end-game. Making it cheap enough for lower level characters would mean it becomes easy to buy and fit out your ideal ship at 50, leading to: "Well... that's my ship done. What now?"
And large guild ships should definitely be expensive, so that guilds genuinely have to pool their credits to afford one. The best guild ships should be so expensive that they are status symbols for the best guilds.
I'm not in a big guild - I'm in a casual guild. I'm a casual player. I'm just smart enough to recognize that you have to provide content for the core playerbase as well as the casuals. The storylines are perfect for players like me that love playing for an hour or two in the evenings, and longer on the weekends. But for players who dedicate significant amounts of time to the game... well they really don't have much other than the same Ops runs again and again, or playing their 1000th game of Huttball. They need something more substantial, that gives them a goal to work towards. Saving up for and customizing the best ships would be a great start.