Yes, always worth it! It's a blast but as many people mentioned above, almost impossible to get in with a car.
I will share though that this entire weekend I have seen openings pop up at Trails end for the 31st if you want to go that route.
We usually stay at the Fort all day on Halloween, because we have 2 cars and don't want to lose our parking spots! LOL! However the few years that we have been in the parks and head back to the Fort on the boat, we have never been asked if were staying there or had anyone check our bands at all. It may also be random checks to keep people on their toes. My kids usually leave at a different time than we do, because they each have friends that stay with us on Halloween night and they prefer driving the golf carts around on that day, rather than be in the parks (all licensed drivers).
As others have mentioned though, you can see the decor almost all month, with it's peak being the week before all the way through a few days after. I'm lazy and leave up Halloween for quite a bit of time before I even begin putting up Christmas! We have way more Halloween stuff than Christmas anyway!
Good luck with whatever you decide, you will still see a decent amount on foot if you can't get a cart but you could also go earlier and rent bikes at the barn, which is a lot of fun too!