It depends on how much time you have. You could spend a week in Sydney or a couple of days. It just depends on how you want to split your time.
FWIW - My feeling is about 3 - 4 days in Sydney to cover the things you've listed, with time to spare. You might want to look at doing a harbour cruise as well.
If the tall ships appeal, let me know. I'm on their mailing list and they do regularly offer discounted cruises.
http://www.sydneytallships.com.au/
Jill - pick the dates that suit you and I'll make it work for me. March 14th is likely to be a public holiday in Victoria; so that could be a good week to take some time off for me.

Food and Wine, Moomba fireworks, Philip Island, Yarra Valley (wineries and Chocolate), City tour, Flower and Garden. And maybe some horse riding.