Ice Assassin and Simulacrum will make the game all about them, if allowed. There are actually a few permutations:
1) The components (piece of the creature, gold, and xp) can be ignored by the usual methods.
Result: Everyone who reaches that level of casting (or Wish-bootstraps their way into it) can have as large an army of arbitrarily powerful creatures as they want.
2) The components can't be ignored by any means. IA is allowed.
Result: Getting pieces of powerful creatures (and making sure nobody gets a piece of you) becomes incredibly important, possibly the biggest focus of the game. People don't have NI armies, but they do have strike teams, especially of any monster that hits above its HD weight class.
3) The components can't be ignored by any means. IA not allowed but Simulacrum is.
Result: Like #2, but because of the half-power thing, someone having a piece of you isn't quite as bad, and your personal minions won't be as strong as the very strongest creatures out there. In this case (and #2), it becomes very important whether the Simulacrum has all the memories of the original (not clear from the spell).
I wouldn't run a game with #1, but I might run one with #2 or #3, if I wanted to make that a major theme of the campaign.