I have to disagree with the costume idea. Each ship should have unique traits, and hopefully ones that isn't limited to consoles or BO slots.
Right now, I feel that the current idea of refitting ships up to 2 Tiers sounds reasonable, older ships like the TOS era really shouldn't be around in the newer battles, because they were decomissioned. So Pre-TNG era ships like the Constellation should be refitable to at most Tier 5, being somewhat still viable. Of course, Cryptic would have to redo where the Nova, Olympic, Sabre, and the Akira get revamped and replaced with Pre-TNG era ships like the Freedom, New Orleans, and the Ambassador.
Perhaps we should make a thread in the shipyard forum and discuss what ship should be at what Tier.
Right now, I think if Cryptic put in a Lt JG Rank and replace that as Tier 2, put in some new content to space things out, its possible things might not be as tricky as they are now.l