Setting aside the scenario of casting 999 gem Utterdarks, this does have the strategic implication that if:
1) You have an "unassailable" AN up
2) You are planning to alchemize large numbers of gems to pearls (large being defined as "large enough to cast a global")
3) You don't have any other globals currently in effect
4) You can afford to wait a turn to use the pearls
...then you might as well cast the global, hoping to knock someone else's global out of the list. You'll get the same number of pearls back as if you had alchemized them (albeit a turn later.)
Ok, so that's still pretty niche.
Also, rdonj, half of 999 is 499.5 - not sure why you'd round that down to 450?