>"can we really afford to do all these things that go on for 10 – 20 years? [...]"
Can we afford not to?
Investiments in pure science are things that can pay, and pay big, bigger than anything, but often only decades in the future. Possibly centuries. Electricity has been a useless toy for a very long time.
Such dividends don't happen on the time scale of a human's life, and therefore we ignore them. But they do happen on the time scale of a nation's life. Even more on the time scale of humanity itself.
We keep considering 5-10 years as the longest "long term", and pass on any investment beyond that... that strategy makes sense for people, but isn't it harming the nation's history-scale economic outlook? We do want our society to still be around in a thousand years' time, don't we? 'cause if we do, getting to work now on something that may result in workable asteroid mining, space solar or moon economy a hundred years from now suddenly makes quite a lot of economic sense.