What I think would really make this game stand out above the others, would be if FC tried to make each profession different from the others. At the moment, they are all nothing but different definitions of the Soldier class.
Where I mention Slot 2, I mean that one, or wherever the Yalmaha or Vehicle usually is placed.
So here are my suggestions, mainly sources of XP:
Adventurer: Exploring. Create a machine called Mapmaker's Terminal, where an Adv with 4-6 playing hours delay between each time can get an item called Map Logger (ready). This item goes in a Slot 2, wich turns it into Map Logger (activated). When it is active, you increase its value by exploring large zones. This item will then be active for 2-3 hours, or when you remove it from your wear, which makes it turn into [i]Map Logger (locked)[/i). This item can then be delivered to Mapmaker's Terminal for an xp reward.
Agent: Assasinations. A random NPC is spawned somewhere, killable only by your AimedShot. If he detects you, your mission instantly fail. An Agent-only terminal will give such missions once or twice a day.
Bureaucrat: Hard one. I don't really have any good idea, except story-oriented Crat-only Meetings.
Doctor: Not so sure about this one either. At least she should be able to manufacture special treatment and nano labs, at low cost. More advanced: Some mobs give diseases when attacking. These lower skills or HP, and is removable only by doctors. A mob can give disease only once a day to avoid camping.
Enforcer: Killing. There should be nothing really special about this class. He'll get XP from killing things, nothing else.
Engineer: Tradeskills. The Engineer should be the true master of tradeskills, probably by making a lot of weapon smithing and such Engy-only. Some real XP-lucrative tradeskills should include NoDrop parts, so that the Engy has to retrieve them himself.
Fixer: I think very much has been done for this class already. Like their own grid and shop. Maybe they should recieve some Fixer-only missions similar to Agent.
Martial Artist: Gaining XP should be most focused on killing. However, to separate them from Enforcers, MAs should be able to meditate. To meditate, you'll have to sit completely still for 3-4 minutes. Chat, being spoken to, being attacked, at all touching the mouse or keyboard should interrupt it. After successfull meditation, the MA can choose between different short-duration features, like increased damage, crit chance, flying, swift running on water, etc...
Meta-Physicist: Tradeskills. Most nano-type tradeskills should be MP only. See Engineer.
Nano Technican : Change his name to Nano Warrior, otherwise leave him like he is (a bit more nano pool or stronger nukes plz).
Soldier: See Enforcer.
Trader: Trading. Make a terminal called Trading Terminal. There all Traders can pick up different items, with different Target Locations. When an item is picked up, character is instantly hit by unbreakable root until item is placed in Slot 2. Furthermore, having this item makes character immune to Beacon Warp, Grid Warp or Warp Time and Space, added to using Grid or Whom-pa. Item has to be delivered to a terminal in the Location zone, where reward is recieved.
Well, that's my opinions, based on what would be rather easy for FunCom to create.