1. Pirates
Hmm, I really thought along the line of them using some kind of weapon system to knock you or more likely your ship out. Then you're a sitting duck and the get on with, well, looting you for the good stuff.
Now, obviously you would need some kind of defense, which we could offer in several flavours. a) a shield that is invulnerable or at least resistent to whatever knocks you out. b) an installed security system that effectively makes it so much harder for them to succesfully get on with looting, but doesn't really do a thing about knocking you out in the first place. (well, that would effectively piss off the rest of the nasties, which kinda could get ugly

. On the other hand - if you pop in the RPG here you could be quite efficient at taking them out on your own as a Fighter, for example. And you could even upgrade the idea of somebody looting you to include stations. With a security system on board your far better protected from being mugged.) c) Have some disguised containers of explosives that look like something valuable and let them loot it - then switch a little button. Get ready to loot them.
2. RPG Element
I don't know Hard Nova (guess I am googling that later

).
But there's still room for RPG. Now taking the Scout/ Recon - he's just better at using his electronics to get out that little bit more of information, knows where to get that little piece of software that makes the static in nebulas a little less, sees a little further with his enhanced display. I don't think that's far from realism. Take a sub - the guy at the sonar knows to differentiate between all this blobs and pings the regular *unexperienced* guy knows as nothing else but blobs and pings.
Now that a trader has some better sources, knows to haggle better - Well, darn me, but I think that should be a given. He's a trader after all.

And the fighter - well, always go for the weak point. But knowing where it is? If you take real life - Kung-Fu dude and regular guy will fight quite differently, even given the same waepons. Comes all down to experience.
Never said anything bout better armor or the likes.

Also - you could split missions based on the path of the character - the fighter gets the missions with all the fighting, the trader gets to be a convoy himself, trying to get essential supplies to that station in dire, the scout gets to go and find the enemy station or some lost cargo... well you get my drift. Each to his specialty.
3. Sideways drive/ directional drives
Well, seeing how there are many many different factions and likely to be more - we wouldn't have everyone using the same thing and tactics.
Regarding realism - I don't really know, never been to space myself and all

(hope this didn't sound condescending (hope this is the right word, english is not my first language))
Either way - I guess if you can have thrust at one end - why not at any of the other. Now - I see the argument of engineering comming up, with all the things I really don't have the slightest clue about - but let me counter-argue or questions: So what?

I'm sure if you can make it one end, you can make it any other way, too, if the price is right.
Even if you scale down the thrust to a third from main thrust for the sidewards (and forwards - there should really be counterthrust) it would be a great improvement for one-directional weapon systems. From personal experience and I'm sure you will agree with me here - when you use a one-directional weapon and, e.g. have the enemy follow you theres always the situation where he's just that little bit off from your weaponsaxle to the side. Now a little thrust sideways and it would be helped.
As for the AI - don't got a clue about this, so *shrug*.
4. Sideways weapons
*ugh* Which ones?
5. Solarcells
Well, I personally don't think the solarcells are in any way overpowered of even remotely close to being so atm. I just think to make them something worth looking at is the option to use them when you need them. Personally I think it is more than likely that if you install some solar cell *hard* in a specific slot that would mean they are plastered to the outside of the ship *d'uh* and therefore if ever you drop your shield and get hit by something - there gone or done for. So I'd rather see them as a deployable sort of array you whip out in dire situations of no-fuel/ reactor failure etc. Maybe it would be wise to make them only produce just enough juice for the bare minimum - lifesupport an just enough engine thrust to get you to the next station.
I have to admit, the first time I played I got into the situation where I had nothing left and died a freezing death in a wide open space.
6. Afterburner
I guess I didn't really get to the point on this one. In SCII the thraddash have this afterburner weapon which - if I rmember this correctly - is a booster that speeds up the ship and ignites some fuel leaving behind the ship a sort of plasma cloud that damages anything that touches is. Kinda a do-it-yourself mind with added bonusses
It's pretty usefull when you have some nasties on your tail and leave them a friendly reminder, that you don't appreciate this. Kinda.