Here is a new idea I had. One big issue with using lower tier ships as you rank up is the limits imposed on your Bridge Officers. If this restriction was removed, older ships (while still disadvantaged) could better be used at higher ranks, making for more diversity in the fleet. I propose the following change.
Bridge Officer stations should be based not on ship, but on the PCs rank and the TYPE of ship, not Tier. So if you have a Science Ship, you get the extra science officer. Etc. The BOs you can use are based on your rank. So the Lt. Rank gets 3 Ensign BOs. the Lt. Cmdr. Rank gets 3 Ensigns and 1 Lt who's type is determined by the Type of ship you are flying.
What do you think? I really enjoy the who Bridge Crew things, but like to have a lot of diversity of starships.
But for all I like the miranda class or even the connie... There's no way they should be able to even scrape the hull of a galaxy, imagine anything even more modern and powerful.
Ah, but there are still things that will keep the lower Tier ships weaker. They generally have less hull, lower base shields, fewer weapons, and limited numbers of consoles. So they will still be weaker, it just won't be because you are limited on the command staff. I really think the command staff options should change with your rank, not the ship tier.