In my opinion, Antwerp is worth at least a quick visit if you're in the area. It doesn't boast many knock-out sites of interest to tourists, but Antwerp is a vibrant, slightly gritty modern city. I imagine if Bruges had not gone into hibernation, it would today probably look and feel much like Antwerp.
What is there to see? If you like art, visit the Reubenshuis. The city's late Gothic cathedral is probably one of the most under-rated in Europe. There's also a nautical museum located in a small castle on the river. And like most old Flemish cities, there's an old Grote Markt lined with elaborately decorated guild houses.
If you want to know about the region's past, visit Bruges. If you want to see it's present and future, visit Antwerp.