Lenses like this, you might not use them for a while, they may sit on the shelf for ages unused, but you're never going to sell them because you're aware of what they can do. Shooting wide open is not what photography is all about but you just can't help it with this lens.
On paper, 58/1.4 gets you as shallow DOF as the 50/1. In practice, the lens design decides if it truly looks "noctilux" tier or not. Judging by the samples here, it looks like to be the case. Not too shabby for a lens that can be had for a couple of hundred euros!