At present, the most impoverished groups in the Soviet Union do not live in the area that HSR will visit. If the HSR has connection, then that means that you are in a place with at least moderate economic value.
The road networks we're talking about are entirely different kind of networks. We're not chosing between connecting the local suburb with a school via 4 lane stroad or sensible tram. It's the difference between an intercity connection between 2 prosperous cities, or a collection of roads to a whole array of towns in the middle of nowhere.
And sure, none of those people in town might be able to afford a car, but the town store is getting it's supply by truck, and when that truck disappears into a mudhole, the prices go up.
Edit : Though our current road projects are not yet getting to nowhere, they are connecting the towns and cities from which the road to the middle of nowhere departs.