Meaning of the dialog in bold and "sour street light"

Question

This passage is from The Children's Bach by Helen Garner

Up there under the leafless vine they were talking. Vicki saw their breath. From the angles of their bodies she could tell they were arguing. Dexter was trying to make Elizabeth do something.

‘It’s not my job,’ she said. ‘Why the hell should I?’

‘Because no-one else will,’ said Dexter. ‘Because there’s nothing else. What else is there? Otherwise we’re all just dry leaves blowing down the gutter.’

Vicki got into the car and kept her face against the side window. She saw sour street lights, a house standing in a junk yard: old washing machines, tea-chests, a car with no wheels. Elizabeth sat silent with folded arms. Dexter sang aloud in a foreign language.

Does the dialog in bold mean "Because no one else will do it. Because we have no other choice, what is the other solution? Otherwise we will become just like dry leaves blowing down the poorest region"?

Does "the gutter" here mean "the poorest region"?

Does "sour street lights" mean:

1. dull looking street lights?

2. very bright street light which your eyes become tired by looking at them?

Answer 1

The gutter is

a channel at the lower edge of a roof for carrying away rain, or a side of a road that is lower than the center of the road, where water and garbage collects:

That is, they become like the leaves, not only after they have fallen off the tree, but when they are clumped up as refuses.

"Sour", on the other hand, reads like a metaphor: she thinks they and their light are unpleasant to see and not (metaphorically) sweet. It is certainly not a common idiom.