There's nothing bad about working for what you get, infact it's preferable, but I don't think random chance is the way to introduce that difficulty. Like Gip0 said - some stuff could be with recipes and materials that you gather overtime. A choice for raid leaders between free for all / master loot and so on, means that pug raids will be extremely unsafe and people would ninja items all the time.
That is why you should prefer to raid with your guild. Plus when you raid with your guild you will get extra bonuses plus drop chance increased. This is how you can force people to make communities and use them. Not just some random people pressing buttons. MMoRPG is a game of a community.
Kind regards,
Armegon.