Depends. Which park? MK ones are likely more valuable than Epcot ones, you can get a good view of IllumiNations in many places.
What else were you planning to use them for? You may not want to give up shorter lines for your preferred attractions.
If you are looking for an uncrowded place to see a MK parade or wishes, no kids on shoulders, nobody standing up next to you and trying to push up into your face, then a parade/Wishes fastpass can be worth its weight in gold. (The parade viewing area is uncrowded but it's not shaded, there are no seats (except on the curb) and it's been noted that while it is directly in front of the castle, it's in a difficult place if you are trying to get both the parade floats and the castle in a photograph. The Wishes area is a side view, not head-on but Tinkerbell flies directly over you if she flies that night.)