As far as how often tomes drop, that depends upon what level U R doing. I do ALOt of <10 quests and have only seen 1 +1 tome. However, some members of my (now former) guild would give me their "excess" tomes all the time. However, they were farming raids and high end content.
As far as Cha vs Wis. Either can be buffed up quite high and cleric is Wis based. So, if U think of a FvS as a Sorc type, Cha would be essential. However, many classes have a "slealth" stat (one that is not apparently primary but very helpful). This is the case with the Paladin (as Cha is the primary stat 4 Undead Hunter) or the Rogue (as Spot is Wis based and U must notice B4 U can find something). Finally, there are "sneaky" ways 2 play toons. There is 1 guy who makes sure to buff his reflex save and take the Evasion chain. Then, just like a rogue, his monk can ignore trap damage!