We are going to be in Vienna for five days (six nights) in July.
I think the Vienna Card would be a bad deal for us. The discounts aren't that large at sights, and we wouldn't use the other discounts at all.
But in 2015 the Vienna Pass came out which looks a little like the Paris or London Passes except that there's less line skipping ability and we would lose the ability to skip the line at the Schonbrunn Palace by using the Vienna Pass rather than buying the Sisi Pass. It also includes four hop-on-off bus lines that cover the outer sights. I've never used a hop-on-off service just ordinary transportation and I don't know if this one is any good.
As to the cost benefit (or loss) I can crunch the numbers and under this plan we would save money even without using the hop-on-off bus service and might drop into some places not on the itinerary. But I don't really know how much time the particular venues take in Vienna. Is this an overly ambitious schedule? If so, the Pass might be a bad idea.
Day One Morning: Do Rick Steve's or other Old Town Walk taking in the Opera House and St. Stephen's (we will probably climb the tower) and Possibly the Mozart House Vienna Museum. Afternoon: Hofburg Imperial Apartments, Treasury, and Palace Museums. Evening after dinner: Self guided joy ride around the Ring.
Day Two Morning: Schonbrunn Palace. Afternoon: Kunsthistoriches Museum, Music Museum, and possibly Leopold Museum. Recuperate in The Palace Gardens.
Day Three Morning: Belvedere Palace (not covered by Pass though we might be tempted to substitute things that are, and there are many other things to see) Afternoon: Kalzplatz Area including the Otto Wagner Pavilion, the Secession, Wien Museum Karlsplatz, and possibly the St. Charles Church Dome. Followed by a stroll through the Naschmarkt.
Days Four and Five Reserved for a day trips though probably really done between days one and two and two and three. One of the ones we were considering is the Carnuntinum which is covered transportation and all by the Pass. The other possible day trips (Melk and Bratslavia) are not covered in any way by the pass.