Turns out that this is how people want to fly spaceships. Slingshot maneuvers and dumping reaction mass make for a great simulation, but not an enjoyable one for most people.
I think space combat in reality would be 99% dull, 1% mind blowing too fast to react insanity, because the firing windows would be so narrow before just being missiles fired back and forth, with point defences having ages to pick down the enemy munitions.
Realistically speaking. Lasers would lead to mirrored ships. Particle beams would likely lead to the magnetic shields proposed for protection against the solar wind. Explosives will be highly inefficient in a vacuum, so they'd only be implemented like in current bunker busters. So we're talking kinetic impact weapons.
I've given this a lot of thought recently, working on my own hard sci-fi space game :)
I don't think mirrors are a good protection against high powered lasers. I've done some reading around the Internet and the consensus was that even if the mirror is absolutely flawless and perfectly clean, it's only a matter of time before a laser punches through it. The best defense against laser weapons turns out to be bad weather, which is hard to find in outer space. (Fighting inside a nebula might help?)
I think beam weapons will be devastatingly effective, once ships have enough power behind them, leading to battles at extreme ranges (light seconds to light minutes), where evasive manuevers can be somewhat effective.
That's my take on it, from reading various Q&A's on the net and thinking a lot about how space battles would probably really work in the near future. It's great fun to think about.
Maybe some kind of gas or mirrored chaff as a countermeasure?
On the upside it's not an atmospheric flight model in Elite. You can orient yourself freely if you're not thrusting, and indeed 'flying backwards' by getting some thrust going and then doing a 180 so you can fire at the enemy with your forward-facing weapons is a pretty essential tactic.