Let's see if I can atleast help on some questions:
1) Every 5th - 10th mob drops a coin... sometimes I get more, sometimes less. I didn't notice a difference between VIP3 and 4 on the coin drop rate.
2) If you have VIP4 and party with someone with VIP0 you have drop chances like VIP2... so, non VIPs drag you down.
There are other optinons that say the last hit would matter... and again other say lat hit matters only on raid bosses....
But the first one is the one that makes sense the most... the other two could be exploitet too easy.
3) Spoil sux no matter what... even with VIP4 was no difference noticable... cuz the rates are just so extremely low. >.<