Celebrim
Legend
The trouble with that is the players become emotionally invested in their ship in the same way that they become invested in their characters. One does not “trade up” the Millennium Falcon or the Enterprise.
Only if your ship is the Millenium Falcon or the Enterprise. You don't become emotionally invested in a garbage scow or a rotten tub. The ship has to be something you have depended on successfully and is well, better than other ships. The Millenium Falcon was legitimately the fastest ship of its size in the galaxy, and it was disguised as a "hunk of junk" to better work as a smuggling vessel. No one expected a cheap budget freighter like a YT-1300 to move like a fast courier, to have aboard an experimental super computer as an astronavigator, or to have a cutting edge hyperdrive. The Constitution class ships were the pride of Star Fleet, the first human designed vessels that could outperform their likely peer level opponents while still banking all the sensors and labs of a Vulcan science vessel. Starfleet only had like 12 of them.
I have done these sort of campaigns before and the ships players get emotionally attached to are the same as magic items that they get emotionally attached to. You don't upgrade Excalibur. You do upgrade a +2 longsword. In fact, in the case of the ships, the PC's may be literally continuously upgrading their prized ships with new capabilities, magical items like fireproof sails, enhanced crews, magical items for the crews, etc. But they are only going to be doing that if the ships is already capable of being "the best" at something. The Paladin was emotionally attached to his advanced frigate of superior design the same way he was emotionally attached to his +5 holy avenger. But that didn't stop him from wanting ships of the line.