Deserve an honest attempt at good answers.
I'm going to give it a go, in three parts.

First:

NASA's approach is at the end of the day to basically design, fund and build what becomes a single proprietary space flight system, shutting out competition..

If NASA can be forced out of this proprietary dominance of space infrastructure, and reshaped into a consumer/end user of commercial space products and services, the demand (That the “proprietary system” serviced) will still exist.

That demand is a market adequately robust to sustain a combination of the new private space enterprises, and core space infrastructure.

Second:

VSE is being killed for partisan reasons, but heh? That's the way they roll inside the beltway.

Regardless of which party rules the White House next, a relabeled, reshuffled “Son of VSE” will at the right moment seem like a great original idea.

Why?

Pork politics? Technological imperative? Manifest destiny?
A casserole of all three.

Third:

Are space budget dollars best spent on unnecessary, wasteful manned missions, or are robotic probes a much more efficient alternative?

When manned exploration of the Solar System gains it's stride, this argument will disappear forever, and robotic probes will proliferate as never before.