Add Unit Combat Veterancy to the game.
What is this Unit Combat Veterancy you speak of? In a nutshell, any given unit gains xp when they enter combat and defeat another unit. After "x" amount of xp has been gained, they gain a rank and with this promotion have a slight increase to their base stats.
i.e. 1 X-Wing squad is created (Rank Private, Level 1, what ever you wish to call it). They then engage in a space battle. Within this match the squad kills 1 Tie squad. Upon defeating the Tie squad they are promoted to (Sergent, Level 2, what have you) and get slight increase to speed, dmg and accuracy.
Veterancy promotion is structured on an increasing xp scale. So even though your promotion from rank 1 to rank 2 may only take 1 unit kill, promotion from rank 2 to rank 3 may require 2-3 unit kills.
This will add a very stratigic aspect to the game, where players will want to manage their units alot more carefully. Sending in a rank 3 unit into combat and loosing it has much more impact than sending in a standard unit which is simply replaced by creation. It also gives players another dimension when creating fleets or ground force platoons and enables tailoring these fleets/platoons to have more veteran forces thus having slightly better fighting power for given battles.