I think that would be better if you did it with mithril, the devs won't like it because if they did this they would lose money but a certain amount of mithril could get you either extra gold bonus in % or a certain amount of gold or maybe something else Not sure lol
No to the xtal one, although really its not much worse then the xtals they buy. No on the quicker regen. The plunder up between 3-5% anything more then that would heavily affect the game for all none spenders