[sushiboat]

The problem with the gem globals is that if you have enough of a particular kind of gem to cast its global, you probably already have a good income of that gem kind. If I have an income of 1 or 2 -- i.e., when a gem-generating spell would help me the most -- the global is much too expensive. Also, most of the gem globals become available at the same time as the other expensive spells I would like to cast. Mother Oak is the exception. Add to these drawbacks the fact that spending the gems for globals does not have guaranteed effects or duration. You could be throwing your gems away, or the global might be cast and then soon replaced or dispelled.