Do you mean each new person should get a new bounty, or all reporters should split the bounty? The latter does not really incentivize much, but the former incentivizes reporters to collude with other reporters (i.e. you find a bug, tell your 40 friends to report the same bug, you get a kickback from all your friends who also reported it. $$$$).
The latter does incentivize everyone who stumbles across the bug to not disclose it. At the same time, it's sad for the original researcher whose bounty gets smaller with every new person stumbling across it.
Higher impact; but if it is just luck you are the first of many to find it and did not invest a lot of work in its discovery is reasonable to pay less.
Under "Closed as dup" system the probability is you get nothing for reporting trivially found bugs. Whilst you are still providing valuable information (that lots of people can find it).
Well i see where you are coming from, the point of bug bounties is to reduce risk to the company not neccesarily to reward effort of the researcher. There is a sense that a bug where you have to be NSA level of skill to find is less likely to be exploitted than a bug that every script-kiddie is stumbling upon.
