I am always concerned when an OP starts off with "Is XXX worth the money?" Whether an experience is worth the cost is a totally subjective matter which can only be answered by the person spending the money.
The best you can do is do a lot of research and then decide for yourself! But, once you have decided to go, don't waste your time at the party adding things up in your head to see if it was worth the money. Just dive into the experience and have a great time. (My advice comes from watching my grandmother judge every event on whether or not it was worth the money. In her mind it never was and she ruined the experience for herself and everyone with her by her continual complaining about how much things cost. She was not a happy person.)
That being said...I love the Halloween party and have been there three times in the past five years!

This year we decided to not use a regular park ticket the day of the party. We are going to the Cape May Cafe character breakfast in the morning and then swim at the hotel in the afternoon. We plan to arrive at the Magic Kingdom right at 4pm to enter with our party tickets.
I usually wear a Halloween t-shirt but nothing too elaborate. Remember that it will most likely be quite HOT...too hot for most Halloween costumes you buy for Michigan! The first year we went the kid's costumes ended up staying in the hotel room because they were just too warm for the evening.
This year we are taking my 4-year old niece for the second year in a row. Last year she wore her Belle costume (from the
Disney store) and that was just perfect.
My advice is to focus on the special events that are happening just for Halloween - the parade, the special shows, the dance, the fireworks. Leave the rides for the other days you are in the park. Exceptions might be the Haunted Mansion and Jungle Cruise...they were a lot of fun during the party.
We usually make a reservation for dinner sometime around 5:30pm which gets us out in plenty of time for the party. FYI, Last year the holding area prior to the party was Frontierland, not Tomorrowland the night we were there. Not sure if that was true for all the party nights or just the date we were there.
I hope you have a wonderful time!
Donna