That was exactly why it rang an alarm bell for me! You wouldn't buy tickets to a concert without listening to any of the band's music before you went!
Thanks so much to everybody for all your responses to my post! My partner and I did end up going to the expo in the end, mostly because we wanted that feeling of 'doing something' positive towards moving, as mentioned by other people here.
We drove for two hours to get there and, frankly, it was rather disappointing. We didn't find the seminars particularly informative, they were basically advertising presentations from people trying to sell you services, (money transfer, migration agents etc). There was one solitary medical recruitment lady there, and we had to queue up for at least 45mins to speak to her. She was friendly and helpful, but the information she gave was easily available on the internet. I walked away feeling that I could have called her company office the next day, from the comfort of my home, and had a very similar conversation without having to queue up for ages.
I think there is a feeling that if you don't go to one of these expos, you might be missing out on some vital nugget of information that will help you move to Australia. The truth is that, with excellent information/advice available on websites like this one, and from the official aussie government sites, you can work it all out for yourself and save the time and money.
On the upside it did give my partner and I, who are usually very busy, a day dedicated to discussing our move, planning our timetable and thinking it all through, which was very helpful (although if we had the time over again, we would set the day aside and stay at home together with cups of tea, our laptop and PIO!).
Thanks again to everyone for your responses and advice
:-)