Middle coach seat is totally unacceptable if you've paid for business class (and you have, even if it's an award ticket). Other's have pointed out the Virgin Australia flight. You should be politely insisting on accommodation in Business Class, either on a Delta flight, or on another carrier (VS, KE, heck, even AF through CDG or something).

Not sure what to say about your Virgin Blue ticket. I thought Delta and Virgin Blue were partners? You may be sort of stuck on that one.