I have the Nikkor AI-s 50mm F1.2. Now it's a different brand, different era of technology, but let me share my take on this.
First of all, I am shooting 35mm, not digital.
The AI-S is not AF. For the most part, I am fine with just manual focus, but when it comes to kids running around, or pets that doesn't sit still, I've had some challenges, so AF is a plus.
one beef I have against cropped sensor cameras is, I cannot really manually focus with the view finder. It's TINY!!! I am pampered with my F501 and F4 full size view finders, so manual focus is feels natural. So if you are using a cropped sensor body, turn the AF on.
Depth of field wise, this is NOT a landscape lens. It is, however, an excellent portrait or still life lens. The depth of field really brings the subject forward. Be careful about pushing the aperture to the extremes as you already know it, but it does offer a much wider range of light conditions you can shoot in.
So is it worth getting a F1.2 or is F1.4 good enough?
Well, for my case, I only got up to ISO400, so F1.2 can be very helpful. Some times, I go to the night market and shoot without a tripod, pushing the shutter speed at 1/60 or 1/125. It's under exposed, but I can make the adjustment in photoshop later and it's been ok so far.
For you folks doing digital, I say it's not as critical. The reason being that modern cameras can do so much better under low lighting situation. You can choose to crank up the ISO setting instead of going for large aperture. It's the cheaper way to go, and you don't get the light distortions.
F1.2 is really an exotic lens, like a Ferrari Enzo. You drive it on the street. You drive fast on the street, but you almost never get to drive REALLY REALLY fast on the street.
I do get the privilege of bragging about owning one. A lot of people don't even know it exists.
I'd say F1.4 is more than enough. That's like the Porsche GT3R equivalent. Performance where you need it.