Whether or not it's worth it depends. If you and your kids are absolutely dying to see a Disney Halloween parade and trick-or-treat in the Magic Kingdom and are willing to pay $67-$105 per person, then go for it. If not, I would pass.
Another thing to consider is how late you will be able to stay. Are your kids old enough to stay up late or will they be done by 9? If you can arrive at 4 and stay until midnight it might be worth it. If you can't, it might not.
We did it once. Our kids had fun, but no more fun than they did any other night in the Magic Kingdom. They were more interested in the rides than in the parade and candy. Not only would we not do it again, we regretted doing it as soon as we realized that we had just paid $300 for a few pieces of candy and a Halloween parade. It felt like a rip-off. But I know I am in the minority. Most people seem to love it. When we were there the the Main Street Electrical Parade ran on nights they didn't have the Halloween Party. We all thought it was much better than the Halloween parade and we didn't have to pay extra to see it.
If you do go, remember you are paying nearly as much--or more depending on the date--for the Halloween party as you would a one day theme park admission. You might consider letting the Halloween Party be your only them park admission for that day (arrive at 4 to take advantage of the time) and doing something other than a theme park earlier that day (water park, Disney Springs, hotel pool, traveling to Orlando).