OH GOD, THIS IS EVERYTHING I EVER WANTED. I am so unlucky sometimes i rage at the game and myself. But i would like to make some additions:
Different cards demand different kill count: 1.5k is ok for some, but some really used should go up as much as 7.5k. I think any RO player understands why. Some cards are very build specific and thus have a very low price/use.
Diferent cards should require different amount of zenny too. The reason is simple, and is the same as above. The ammount should start at 200k, in my opinion.
Casual players deserve (a bit) of love too, they are necessary to make the server populated. For this, i suggest making it a higher space of time. Maybe give players from 2 to 4 weeks, which would vary by the same mean as different kill count for each card.
In the same branch, i belive it would be better to make this usable only once or twice per week, i know this may not be interesting for hardcore players at first, but if people drop too much cards, it will reduce what they are worth in the market and when you happen to have a full build, you will understand the disavantage when trying to sell.
It wouldnt be hard to make similar monster, which drop the same card, pull each other ID in order to count them all to the kill count.
There is also a few points i have think of, but am not really sure:
Make the quest acc wide, so this makes that kill counts with diferent characters will add up and even then you cant make it many times with the same account.
Maybe cards adquired this way could be untradable. If you drop a card in the process, it would be normal. Unfortunately, this would make the game more solo, thus, i think in the end its bad for the community.