Cafe Sperl definitely wasn't on my final list of places in Vienna. I had noted in my Rough Guide that it had "decent" food (and coffee) but there were other things higher up for the two days there. Funnily enough the reason I ended up there was because I met another backpacker in the hostel and she said it was on her list more for the atmosphere as being one of the historical cafes in town.
I'd already taken down Figlmuller and Steirereck, and the foodhall of Julius Meinl was more a place for upmarket expensive gourmet items rather than a meal place in itself. So I thought why not?
The cafe does have a remarkably ornate interior and I can see why people come here. Next to us sat an older couple who were more surprised by my new friend's ability to speak German than us being there.
We ended up sharing Tafelspitz (boiled beef, potato hash, carrot) and apparently the national dish of Austria. Cafe Sperl may have even won some national awards for the best version back in the 1990s or early 2000s. The dish was nice and the meat soft, but overall I couldn't see the big appeal of it. It's possible the unexpected social nature of the meal disturbed my opinion.
I wouldn't mind coming back again and trying it again.