I, like many players, paid for a fourth character when I decided I wanted to play around with different designs. A Deuman and two CASTS were my first three, so I did the logical thing and paid for a fourth. Now I am reluctant to delete my fourth to try playing in another Ship because if I do, I lose the fourth character slot until I buy it again.
I get why there is a character limit; to prevent meseta/item farmers, and to mitigate bots, but making players buy the same slot over and over again seems awfully arbitrary.
From the money side of things, increase the character limit; there are enough mad lads out there who will gleefully pay for 24 characters, but find it degrading that they have to buy the same slots over and over.