While added range, opportunity fire, remove mp after fire are all good ideas I have an even better one.
If my idea can't be implemented (or is just to much work) I would vote for opportunity fire first, added range second and killmove not at all. Anyone ever seen a vetnavy battleship stop dead after it fires it's guns? No? Didn't think so.
Here's my idea:
Make combat simultaneous. Both sides move and shoot at the same time. First there's an order phase where all sides give movement, targeting and firing orders at the same time. Then there's a move/fire phase in which movement occurs and fire happens when the targeted enemy comes into range. We would of course need primary, secondary and tertiary firing orders in case the primary target moves away and the secondary comes closer. We would also need to introduce speed as opposed to movementpoints so fighters and faster ships can actually move up close to the big boys. No fun if they can only move one square/turn. That's the bare bones of my idea but it needs to be fleshed out. But think about, it would solve alot of problems and also eliminate the "pick a victim and pound it until it dies" syndrome we have now. We would have to decide if we want to make absolutely sure we kill a target and do some massive overkill on it or spread our fire in hopes of damaging as many targets as possible. Formations would also be more important for mutual point defense support.
Which brings up another point. I want some kind of combat command net and point defense net like in David Webers Honor Harrington books. A flagship that calls the shots and all ships tracking systems are working together to get better firing solutions on seekers, ships and fighters. Task Groups of smaller ships with their own flagships and so on. Several levels of course. The higher the level the more ships can be in it. Bust the flagship (unknown to the enemy which it is btw) and you get a turn of confusion until a new flagship can be assigned. Bust a ships communication net components and it falls out of the net and fight on it's on. Well, you get the idea, especially if you have read the books. But I'm wandering off topic so I'll stop here.