Here's a thought: should there be a Detect Curse spell, or should that be folded into Detect Evil?
The description of Detect Evil is "A spell to detect evil thought or intent in any creature or evilly enchanted object." Doesn't appear to cover a curse, unless it's part of the evil enchantment on an object. A curse placed on a person would not be detected.
If you keep the two ideas separate, then it should be possible to find or research a 2nd level Detect Curse spell. Not necessarily a high-demand spell, but there it is.
If you roll Detect Curse into Detect Evil, however, you have the option of not distinguishing between evil people and cursed people. That's perhaps unfair, but on the other hand, it slows down the murderhoboes who kill anything that "pings evil".
You could allow clerics the ability to distinguish between the two, or make it a function of level (caster level > level of evil creature means caster can tell it's the creature specifically that's evil, not just an evil in or around them.)