Like Jive said, using a class system wouldn't seem like Nova or EV at all. I'd like a system like this:
Don't have "levels" in the way it's mostly used, but base the "Skills" a player has on the way he plays.
EX: Let's say you have following skill-threads:
Combat raised every time a subskill get's better. Allows you to buy "Combat"-Class ships
->Missile weapons (increases the effectivity of: Rockets, Missiles, Bombs etc)
->Energy weapons (increases the effectivity of: Blasters, Beams etc)
->Defensive tech. (increases the effectivity of: Scan/Missile Jammers, Shield upgrades, "Stun"<f.i. ionizing>)
Trading raised every time a subskill get's better. Allows you to buy "Trading"-Class ships
->Bargaining (buy/sell trade goods for better Profit- only works with Trade Goods, not with Equipment)
->Traveling (increases the effectivity of: Travel upgrades, also slightly increases the Speed while Hyperspace traveling)
->Mining (increases the effectivity of: Resource gaining equipment)
Diplomatics raised every time a subskill get's better. Allows you to buy "Interceptor/Diplomatics"-Class ships
->Scanning Tech (increases the effectivity of: Scanners etc)
->[Diplomatics, don't know a name

] (let's you fly through all Territories in which you are not KoS <even if you are disliked>)
->Something else...
Illegal raised every time a subskill get's better. Allows you to buy "Pirate"-Class ships and some other licensed ships, but more expensive than if you had the right license, and only at certain stations.
-> [Player can equip Scanners that scan another player's cargo hold]
Is set to 1 when the Player is KoS with at least 1 Govt.-> Something else...
-> Something else...
Now, if a player often uses a Light Blaster(successfully, shooting into nowhere is useless), his "Energy Weapons" Skill is being increased. All Skills start at 0 and can be raised to Max. 15 (in my example..), only one Skill in every Thread can be raised to 15 and only 3 in all threads can be higher than 10.
There are no "Skill Trainers", skills can only be raised by using them. Exception could be the Illegal skills that could be "bought" at Pirate Stations.
Equipment could have a "level", if your Skill is lower than this level, you can still use the weapon, but with big Mali, like, on a weapon, slower reload, more energy drain, worse aiming...
You could prevent special Items from being bought by new players by making them require a higher rating at the government.
Ok, that's it for now. I hope that wasn't too much, but i guess Tips are always welcome

-Lukas
You shouldnt have exp or levels in the normal sence. Like in EVN every kill and action relating to a govermant will increase an invisible number. When the number gets to a certian point you will get a title such as deadly. This will only affected how npc act towards you (such as attacking on sight or praising and being a annoying fan)(you may want to chuck in a fame state as well). Any different player will be able to use a screen to see another players titles, name and ship(only the ships type(hull)). And combat, trading and other such things are only governed by a player skill with the game rather than stats(especialy combat). And the only limit to a ships ability is money and avialibility.