I think judgments about things like that are between you and God (or Whomever). If it's justified, then you should have the blessing of your Higher Self and the Higher Power. No one on this website, or really anyone, can tell you if it's justified or worthwhile.
Is it justified and worthwhile to you? Do you feel like doling out punishment? Being the judge, jury, and executioner? Know that many people in probably similar situations to yours have chosen both paths - some will choose to throw a wrathful curse and never regret it even for a second; others will turn the other cheek and feel strengthened and uplifted by their decision. I have done both myself.
People have varied opinions on karma and magic. You will find both viewpoints argued passionately on this website. Remeber that The Threefold Rule is a part of Wiccan religious dogma - not a belief of all (or most) magical pracitioners adhere to.
Also remember that karma is a part of Eastern religious dogma. It is bastardized ad nauseum by New Agers, but must be differentiated from the Law of Return. Karma is something that's worked out over lifetimes, sometimes through a complex caste system, sometimes through reincarnation, certainly tied to your family and ancestors - karma is not "i do something bad, then something bad happens to me," or "if i do a money spell, some rich relative will die," etc.