Vienna Pass, yay or nay?

This depends to a considerable degree on what type of sightseer you are. Do you have a long list of attractions you want to visit that you have to cram into too-few days? If so, I suppose the pass might pay off. However, if part of the reason you're considering the pass is that you like the idea of flashing it and walking right past the ticket counter, check the websites of the places you expect to use it. Many of them may currently be requiring pre-booked admission times.

I've decided big-city passes are not right for me. That's partly because I tend to go all-in when I visit a museum or historic site. If I'm not interested enough to spend considerable time there, I simply skip it and use the time elsewhere. These are factors that might apply to other, more typical travelers:

• In estimating how much time you'll actually have for visiting covered attractions, don't forget that at some point you need to take time out to eat. If attractions are not close together, time will also be lost moving between them. You may well not have enough time to cover as much as you think you will.
• Will you feel you can't explore an interesting street or neighborhood you come across while the pass is running? Is that the way you want to travel?
• In some markets (I don't know whether Vienna is one of them), some attractions sell on-line tickets at a slight discount. That discounted price will not be reflected in the promotional material purporting to show you how much you can save with the pass. There are sometimes senior discounts as well, and there are virtually always discounts for children and students.
• Are there things you want to do that are either free or not covered by the card? Will you be visiting them during the card's validity period? That will reduce the likelihood that the card will pay off.
• If your target list includes a mix of covered and non-covered sights and you plan to buy a card covering only part of your time in Vienna, you will probably have a choice between maximizing card usage (hitting only covered sights during the validity period) or efficient sightseeing. To be efficient, you need to group sights geographically, which often means mixing covered and non-covered sights on the same day and not getting full use of the card.
• As mentioned above, if convenience is a major plus factor for you, verify on the official websites of museums, etc., that the card is going to work the way cards used to, pre-COVID.
• Even before COVID most significant attractions sold tickets online--sometimes with fixed entry times, sometimes without. This means you don't have a binary choice of buying the card vs. standing in line. You can almost certainly buy individual tickets to all the busy attractions online before arriving in Vienna. A pre-purchased entry ticket will allow you to skip the ticket-buying line.
• If inclusion of local transportation as a card benefit is a major factor for you, be aware that virtually every city of any size sells stand-alone transit passes. Usually there's a one-day ticket and at least one longer-term ticket. In addition, if you think you're going to get a great deal of use out of the transit benefit, keep in mind that while you're sitting on a transit vehicle, you are not using the sightseeing benefits of the card.

I honestly think the financial part of this decision isn't terribly crucial. I believe the vast majority of travelers who buy city sightseeing passes don't save money. And I assume most who opt for passes don't lose much money, either, because those are travelers who are attracted to the idea of seeing a lot of places and will get more use out of the pass than I would. I think the way a pass tends to distort ones sightseeing itinerary (encouraging the visitor to hop between covered sights while skipping over other nearby attractions) is a bigger issue.

A number of years ago, an agent, in the TI office, told us we were better off buying senior transportation passes than buying the Vienna pass. I have found that such city passes often include many attractions that aren’t of the slightest interest to me. When you figure out which sights you actually want to see, the savings may be negligible.
The other advantage, sometimes conferred by such passes, is being able to skip entry purchase lines. I should think that long lines in Vienna, in September, would not be too likely.
At any rate, if you do decide to buy, I think you can wait. No reason to buy now.

Thanks, sounds like no need. We want to do Schonbrun and Hofburg but not much more. We’re staying near Stephanplatz so will see the church. We like to wander too. Thanks for the answers. Hard to believe I have been to over 50 countries but have never made it to Austria!

Also see if the if you can observe a rehearsal for the Spanish Riding School. That was a highlight for us. And Schoenbrun has a zoo on it's grounds if you are into zoos..

If you’re only planning on Schönbrunn and Hofburg, then the answer is “nay” as you’ve deduced. On that note, I usually recommend that visitors pick either Schönbrunn or Hofburg to see on the inside, but not both. So much more to see, especially out in the open.