It's hard to know the ideal time to upgrade one's TV. Usually, you just wait until it breaks down out of warranty, but if a good deal for a larger screen pops up, it's OK to consider a replacement based purely on inches. Bing Lee is currently offering a great price on Samsung's 60-inch Series 6 3D LED TV, if you have a spare $1500 you don't mind parting with.
The deal, spotted by OzBargain user "argus", provides free delivery if you live in the ACT or the Sydney metropolitan area. If you reside elsewhere, you'll need to add an extra $40.
Alternatively, you can hit up BigBrownBox, which has the TV for the same price, but will post you your purchase free Australia-wide. Note that when I checked delivery for Melbourne, only one TV was left in stock. Putting in a Sydney postcode however showed no warning.
Samsung UA60H6400 60" 152cm 3D Full HD Smart LED LCD TV [BigBrownBox, via OzBargain]