When I was President of SFWA in the early 70’s Norman Spinrad and I counted 19 people who make a living at SF, and those included Asimov who hadn’t written an SF in years — he was writing non-fiction — but was of course known as an SF writer, and Larry Niven who made enough that he could have lived on the income, but in fact was living off his trust fund, having chosen the right great-grandparents. And of course Silverberg by then was living off his investments…
Lucifer’s Hammer by Larry Niven and me broke out of category and stayed 14 weeks as #2 on the NYT best seller list, and that did seem to help sell SF. But the boom and bust cycle has been going on since at least the 1960’s when I began to keep track of it. After Hammer and some other best sellers SF boomed and got a lot of paperback rack space, and there came a new golden age for SF writers.
Now, of course in today’s economy, with the collapse of the paperback book distribution system and the rise of eBooks everything is changing again.
There have always been a few best selling writers who make a living at it. What seems to be vanishing is the mid-list writer who does a really good book every few years — John Boyd comes to mind for some reason — and who didn’t live splendidly but did manage to make a living. Some were academics, some were full time authors but eked out their incomes with literary teas and honoraria as guest lecturers at creative writing classes. Most of those are gone as the mid-list collapsed.
I have done well as a writer, but I would sure hate to be breaking into this game now.