...exhibitors rank the purchasing influence and buying power of attendees as the top factors when deciding whether to exhibit at a given event.

I would take quality over quantity every time.

The Trade Show Calendar is a great site to find out valuable information about shows.  It also allows you to sort by many categories and add information about a show.  You'll want to add that site to your favorites.

Make sure to qualify your business to business lead generation strategy by contacting the show management and asking for data that they have collected over the last few years.  How many people are already signed up for a show is an indicator of its strength.