Josh Hausman emails:
You're absolutely right that insofar as the Veteran's Bonus has a relatively small impact on the long-run budget situation (since much of it was going to be paid in 1945 in any case), the marginal propensities to consume that I find are that much more impressive. In terms of comparing this to Miles Kimball's proposal, the 1931 loans against the bonus are the cleanest comparison, since all that happened then is that veterans were allowed to borrow against their bonus. Since they were charged interest, it cost the federal government absolutely nothing.
The 1936 bonus is a little more complicated. Much of it was just giving veterans money that they otherwise would have gotten in 1945. But there was some hit to the long-run federal budget since part of the bill was a sizable forgiveness of interest on the 1931 loans. Also, veterans got in 1936 the same amount they were going to get in 1945, so the federal government lost 9 years of interest on that sum.