Here’s Von Neumann’s response to straying from pure mathematics:
“[M]athematical ideas originate in empirics, although the genealogy is sometimes long and obscure. But, once they are so conceived, the subject begins to live a peculiar life of its own and is better compared to a creative one, governed by almost entirely aesthetic considerations, than to anything else, and, in particular, to an empirical science. There is, however, a further point which, I believe, needs stressing. As a mathematical discipline travels far from its empirical source, or still more, if it is a second and third generation only indirectly inspired by ideas coming from ‘reality’, it is beset with very grave dangers. It becomes more and more purely aestheticising, more and more purely l’art pour l’art. This need not be bad, if the field is surrounded by correlated subjects, which still have closer empirical connections, or if the discipline is under the influence of men with an exceptionally well-developed taste. But there is a grave danger that the subject will develop along the line of least resistance, that the stream, so far from its source, will separate into a multitude of insignificant branches, and that the discipline will become a disorganised mass of details and complexities. In other words, at a great distance from its empirical source, or after much ‘abstract’ inbreeding, a mathematical subject is in danger of degeneration.”
Thanks to James Lee for pointing this out.
Scientific Clearing House 
Seems relevant that in his book “The Computer and the Brain”, von Neumann says of neuroscience, “It may alter the way we look at mathematics and logic proper.” BTW, the book is now in it’s 3rd edition with a new foreward by Kurzweil that points out that von Neumann asserted the possibility of a singularity (using that exact term!). Personally, I doubt that von Neumann would share Kurzweil’s complete vision on the singularity.
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