Crap, I've been using this little trick since it came to me almost immediately when playing my first game. I put at least one emergency propulsion component in every ship I can and then build at least one repair ship doubling as a troop carrier to travel along with the fleet (also with emergency propulsion). You get to use the extra propulsion every turn since the repair ships will repair the whole fleet's components each turn. Try combining colony ships with this idea and you can really spread out fast. I also use this concept for boarding ships. With repair you can board a new ship each turn without having to return to a spaceyard to repair the boarding party components. With a emergency propulsion or two thrown in, no ship or planet is safe. You can zoom in from a full system or two away and take any planet or ship (I love troops and capturing worlds intact) I do like having these self sufficent fleets.
Now, did you have to go and speak up and share this neat tactic with everyone? They'll take away our shiny new toy.
Seriously though, humans will always be able to come up with slime tactics like this. Finding them is a lot of the fun in playing the game. I remember playing Conquered Kingdoms by QQP (great game) and discovering the "Double Wizard Fireball" tactic. Poor AI didn't know what hit it. I could mention the sneaky stuff you can do with combo tractor and repulsor beams but I'm sure most have figured that out already.
Maybe this stuff does unbalance the game but it sure is fun and the AI can't seem to put up a decent struggle straight up anyway so what's the difference?