If you are staying at a hotel next to a station then I guess there is some point to this, but if not do yourself a favour and just take a picture of it as it passes overhead. We made the mistake of buying a Supervoucher day pass, but only because it went past our hotel and you get a book of vouchers for places we were planning on visitting. It basically does a loop that takes in Darling Harbour, the AMP Tower and ... well to be frank not alot more, and as you can walk from Darling Harbour in about 5 minutes there really is little point.
Unique Suggestions: If you do go on this, make sure you do the full loop. It will only take about 15 minutes in total and at least you can say you've done it ... not that anyone will care. The discounts though are good for things like the Aquarium and Seacat rides, so we still saved money as a result.
Fun Alternatives: Walk.
The monorail could've been such a good idea. I think it was supposed to go all the way down to Circular Quay, but instead it goes around the most useless parts of town. I suppose it gets you to the Darling Harbour and the Car parks, and to Pitt St Mall, but that's about it. One of the stops has even closed down, as the building it's in is deserted.
Unique Suggestions: A monorail pub crawl could be good, but I think you could walk it, and save your money for drinks!
Fun Alternatives: Um, walk?!?! Basically you'd be better off.
$4 for a 15 minute ride, for a different view of Sydney. Alright, you get to see the city, but so what. Scratchy and dirty windows make photographing impossible. This thing is best avoided.
Unique Suggestions: Don't expect too much.
Fun Alternatives: If you need to get from one end of the city to the other, walk! If you just want to take this trip as a nice intro to Sydney and don't mind the price, fine.