Perhaps make it that people must spend a certain amount of time in the invance, or they get no exp - e.g. at least 50%? Rules about not AFKing in the invance obviously still apply.
There seem to be players constantly restocking - either they don't have enough EMU to make a decent contribution to the invance, or they are constantly dead. One could argue that both constitute not helping.
On the restocking note, there's what I'd term "inappropriate restocking" - I get the feeling there are certain players who will "restock" after only a minute or two of fighting, which would suggest they are in fact doing... not a fat lot.
I would suggest 50% attendance in an invance, appropriate preparation for the invance (teleport methods in case of death or restock) should mean that players can achieve this, and if not, they are not ready to invance.
So, what constitutes "help"?
* Rangers slinging at least their minimum contribution of arrows.
* Healing players, harming monsters with magic.
* Any hand-to-hand combat with monsters.
* A player to stand at the gate.
I'm quite sure I have not covered all points, so tried to think of a more loose definition of help - "that which benefits the team". Clearly excessive restocking etc do not come under this. I occassionally see players standing round in a moment of "There. I killed it.", which is a normal reaction, but I think people have to bear in mind that time is of the essence.
Even "that which benefits the team" is not a good enough definition, though. There needs to be a clearly defined armour/weaponry requirement for fighters, not just a minimum ranging requirement (300 arrows, AP for certain invance, level 20+). It is unfair to expect rangers to blow 10k+ on arrows, while fighters bring a few essences/SRs and get almost exactly the same reward (I know someone will pick me up and mention deaths/breakages).
I would be all for getting rid of drops, to be honest. Particularly in 40-60, there was a certain player (I shall name no names ) who hoovered the floor of every bone, piece of meat and bloodstained panther fur that there was to be had. I'm sure this player had a great time in invances, but it's plain to see his/her actions were purely self-interested and not "that which benefits the team".