OP, I have been wondering and debating this a lot. We had it last time (Oct 07) and used the special entrance, even, but it didn't seem like it was that great, we just knew we had seats. This time I decided to skip it since DD wanted to try Sci-Fi. Now I'm getting worried. I really want to see the show!
I guess I'll just plan on waiting 90 min or more.

I don't think with the FP you'll need to wait that long, they say you only have to be there 30 min ahead. I AM having trouble picturing what it will be like for you having your seats reserved, arriving 30 min ahead, but still being stuck in the throng at the back trying to get someone's attention -- "hey, someone, anyone, I have the package!" When you do finally get in, I'm sure you'd be guaranteed a seat. If there are none left, a CM will probably clear some seats for you in the reserved section (a little old lady with a walker, or a single mom with 2 toddlers, come to mind) and make them stand in the back.

That would be my luck!

I know I'm being way overly dramatic, but Disney really needs to get a handle on this! Robo posted not too long ago that they may re-open the other entrance. Don't know where he gets his info, but he's usually right!
Anyway, hopefully someone who's done it will get on and let you (us) know how well it's working these days.