Casting a spell is an expression of character. Less so than for the sorcerer, since the magic is more distant for the cleric and the wizard, both of whom could cast a spell repugnant to their very nature at need -- if their characters were properly delineated to give them the strength of will to do so. But their choices should reflect their characters. Starting with their domains. But literally, a cleric with the domain of liberation can freely cast "hold person" and one with light can cast darkness. . . just as a wizard who specializes in enchantments can load up with abjuration spells, and vice versa.
Some might be interesting, but it would certainly take up a lot of the story precisely because it's not something that can be dealt with both well and briefly. BUT -- a limited spell list does limit how much you can vary them.
