Ships lvls
An idear hit me when dchan1936 mentioned refits in one of the other posts. Why not have it so that when a ship lvl's up a "new" item is added onto the ships, like a new wing secion, a battle bridge or shield generators attached to the hulls. As the lvl progresses the ship gets stronger, but there is no physical change to show that appart from the lvl marker that tells you what lvl your ship is.