OMI, no. Well, at least not the ones with a paid ticket. If you will be staying at a deluxe WDW hotel, then the extra PM park hours are worthwhile (but HS is not typically one of the parks.)
One aspect of the party events is that the weather in the summer/early fall can be iffy with rain. Last year, we felt bad because people going to a Halloween party at MK were stuck going on a night with absolute pouring rain all night.
(That is one thing I don't like about paying for G+ a week in advance.)
During the extra PM hours, it still took time to clear out the queues in HS, so the first 30min many rides had considerable waits, but towards the end of the night there was a drop-off. The paid party might be a little different where people feel obligated to stay.