I wouldn't say that the 1.4 vs 1.8 is the only difference. The 1.4 has way better build quality, the 1.8 feels like a plastic toy. And the 1.4 is sharper at bigger apertures. If you primarily are going to use it for low light, I would definitely get the 1.4. Is it worth the bigger price tag...
1. Isn't in focus and isn't interesting. Just a snap shot of a cool lookin' flower.
The rest aren't very sharp and don't really have a subject point.
The building shots would have been a whole lot cooler if you backed up and captured more of the building.