Keep in mind when deciding what the play experience is going to be like who your market is composed of. Unlike any other MMO out there you can tap fan's of a franchise unlike any other in history. The Star Trek Fan tends to have the same optimistic outlook on the possibilities for the future that the shows have. Models that tweak economies in other F2P MMO's to get players to spend money to avoid aggravation will have a negative total effect on long term revenue from Star Trek Fans.
Getting a new ship at each rank is the hallmark of what ranking up means and is one of the things that makes this game fun with anticipation of each level. Word of mouth in the Star Trek community is one of your best marketing tools to spread the word about how cool this game is. Trust us when we the players who have been here since the beginning tell you that taking away the ability to get a new ship on leveling will turn off many Trek fans. They will likely quit before they have time to become aware of the depth of trek lore you have so lovingly worked into the game that is the true hook for fans. Star Trek fans spend money on their fandom (attend a convention sometime). Get them hooked on the complete game and they will add c-store points steadily over the long haul. Attempt to manipulate them into it early on just to get the next rank ship and watch us recommend to the entire trek community that you might want to skip trying it out because of the frustration you will have just trying to equip your character.
The (hopefully bright) future of STO depends on Star Trek Fans, not just any old MMO player base. We tend to be educated, older, and just a bit critical of annoyances. Make the new fans who show up to try F2P STO love the game from the beginning without any financial commitment and you will hook them for the long term.