1. Make fleet actions available for all levels through admiral. Give each a level range so everyone has a fleet action playground - but let players choose whether to enter levels above or below their tier.
2. Make instances of fleet actions which can have both factions present and let players choose which to enter.
3. Players outside of the level range get no loot drops: If you are there to participate in fleet activities, help friends, or even strut around stroking your ego in a ship 30 levels above everyone else fine and good for you. Feel free to do so and have a great time - and I do really mean that. This is entertainment. Please no excuses from players farming loot drops for their other characters or friends.
Just to highlight how little of a problem this is, you gain much better loot as you progress throughout the game so high level players aren't exactly stealing anything of significant worth. You'll also likely find that high level players don't want that loot so you could actually ask them for it. I personally would gladly give up low level loot I don't want.
Your most likely missing a shield battery or along those lines so try not to stress over it.
Just did 3 fleet actions this evening. I'm LC5 which was about average level for those areas I was in. We had everyone from LTs to admirals in there. It was fun. I enjoyed seeing everyone working together like that.
I don't really understand the worry people have about loot in this game. It isn't the type of "must have" loot that other MMOs have.
As for Starbase 24, you're not going to be in that level of ship long enough to worry too much about loot items. Mirandas get replaced pretty quick.