I have to say I miss Hogan also. My wife and I have also read most of Hogan's books and thoroughly enjoyed them. We are currently introducing our youngest to Hogan by reading Code of the Lifemaker as a family. His writing was not as good near the end and in all he did not publish near enough for my liking. I've yet to find a similar author to replace him in my library. If you have any suggestions I'd be interested in hearing them.
That all said, I had not heard of Velikovsky or John Ackerman... will have to check them out.