I know everyone's experience is different - but for what it's worth: when I was planning my Sept trip, Y&Y was the only restaurant for which I really had a hard time getting an ADR. I used a reservation tracker and one popped up the week I traveled (left on a Tuesday, ADR was for Friday). That said, I had the Landry's SC card and wasn't worried - but I did get the sense that they just didn't have a ton of openings.
The card definitely works (I too worried that it might be a pixie dust type of thing). I originally had an ADR for something like 3:45 (I was aiming for an early dinner before going to Boo Bash for the night). I ended up being exhausted (I may have dozed off during the Navi River Journey, lol) but really wanted to eat at Y&Y (in part because I'm cheap, er frugal, and had an expiring birthday credit from Landry's SC). So, I decided to leave DAK early to get some rest before BB and decided to stop by Y&Y to see if they could get me in early and/or cancel my ADR without the no-show fee. There was a moderate walk-up wait (I overheard 45-60 min for some tables of 3-6). They ended up cancelling my ADR and walking me in with the LSC (although after that happened, it sort of messed up the system and the manager discouraged the CM from doing that, showing a way they could move up the ADR) and I waited 5 minutes at most (table of 1, fwiw).