Supposedly, using these cards to enhance cards results in a larger bonus, and from what others seem to have gathered, if you use them to boost a card of same alignment, such as Demon for Demon and God for God, should boost that bonus even more. They are basically enhance or trade fodder, as they can't be used to battle, and with only 100ATK and 100DEF MAXED, they'd be useless anyway. And I believe the way it works is if you enhance a card that has a skill, with a card that has a skill, such as Demon Queen, you increase the chance of having that card's Skill Level increasing. Increased Skill Levels seem to increase the odds of skills going off in battle.
I love gold dragon's, well finding them *laughs* they sell for 30,000 rupies each... I've been trading my gold dragon's for cure waters makes it easier to trade with some people harder with others but eh.
Angel Queen's not really used these yet, but they do seem to give a nice boost to cards when you enhance... Had to use one with a few high normals I had and it was like 500%+ which was really really good.
Evil Queen is more useful i think as it when used it gives you a better chance of increasing the enhance card skill level. I have not used this yet but some have said that it can even give more than one level.
As far as these three go... I always trade for the queen's allot of people do so if your not going to use them find someone like me and make em pay hahaha