From: Sander Vesik <sander@haldjas.folklore.ee>
In this regard you are almost as bad as Oberg - while he claims with
no real reasoning that no civilisation will ever do anything
significant in space you have the opposite endency - claiming that
its manifest destiny of teh first civilisation to conquer the galaxy.

I take a middle road: Any civilization that develops technology capable
of transmitting radio, probably has a problem with population exceeding
the planet's resources, and probably has capability of space travel at
least for automated probes within their planetary system. Accordingly
such a civilization either would fail to solve the resource problem
before their society goes into global decay and ceases to have radio
capability, or builds solar-power collectors around their star to
supply more energy to run a more material-efficient civilization. Given
that, they are also likely to develop off-world colonies. The result of
all this will be a loose Dyson sphere. Whether they then send any
probes to other stars, or sit content that they have immense energy for
their single-star-system society for the next several billion years,
I'm undecided. But the fact we don't observe any Dyson spheres within
our own galaxy shows that no such civilization exists, i.e. we are the
only currently extant technological civilization in our galaxy.

this assumes that 'move to another star' is a potential niche

Once Dyson-sphere technology exists, putting a colony around another
star is definitely a potential niche. The only problem is getting
there. We have some ideas for doing that, but we aren't sure they'd
really work. But for purpose of SETI, this is moot if there are no
Dyson spheres hence no advanced civilization whatsoever.

Or maybe they are made up solely of people like you and Oberg and
never actually accomplish anything

Unlikely. There'd be haves and have-nots, and the haves would arrange
to use available planetary resources to get the solar power satellites
started before too long, because they want to have more.