For my wife and me, it is unquestionably worth it. We have a blast every year, and we're already looking forward to next year. If you already like halloween events, then you really should try it. Watch a few youtube videos to see what the scare zones are like. There's a few indoor videos of houses (edited to not show the entire house) too, but the videos are usually too dark. There's some funny videos from the Ellen show where a couple of staff members go through a house (note: in the Ellen videos, the people go through alone. In reality, there is a continuous conga line of people going through the houses). The sets, costumes, makeup, and effects are so well done, and it is all a very impressive event.
As for going solo, if you are the type to strike up a conversation in line, then don't worry about being solo. If you don't talk to strangers in line, then that would be an additional reason to get the express pass (5-15 minutes wait in line vs 15-120 minutes in standby).
Either way, express pass is very nice to have. So much so that we already include express in our budgeting, since we only go with express (Frequent Fear with Express).
I just re-read the OP and it sounds like you'll be doing a full day at the parks. Yet another reason to get express is you will take fewer steps and be able to see everything in much less time.