I think there could be other things that people could spend their credits on besides introducing power creep. Vanity especially.
A retextured ship that has a specific, unique-ish or interesting/pretty design. See Widow's eagle reskins or the Chimmy with republic v exiles variants.
Unique, new engines (like blackmarkets are to sirian ones).
Special lights with unique effects (like the ALG Mover having fumes coming out of a light spot).
Weapons. Pretty weapons. Like codenames, but really just designed completely for maximum aesthetics.
Thruster alternatives, like the old nomad thruster effect for current ships with the same stats as a Cheetah or something.
All these things, plus whatever people can imagine. It would add variety, wouldn't break balance, and give people something to work toward.
And by work toward, I mean these things should be more expensive than a battleship or something.