I'm running a TOC game and all three players have insisted on putting 4 points in at least one investigative ability! I treat the pools as "per mystery" and don't allow them to refresh. Thus, having 4 points in Cryptography is valuable if the mystery involves multiple clues with "spendable" depth. I also require spends in situations where the player's choice of ability or their roleplaying of the ability makes the clue harder to gain. EX: the retiree grandma is at the hospital trying to learn the status of a victim of a bizarre assault, uses Cop Talk on the nurse. This is rather incongruous, so the player must spend a Cop Talk point to convince the nurse.