>Back in 1865, it was obvious to every-one that the increased efficiency of steam engines would lead to a reduced demand for coal. Jevons pointed out that increased efficiency makes steam power cheaper.

Well, in that case you're talking about an entirely different phenomenon. Jevons's paradox (as defined by this post) happens when the cost of a resource decreases and the spend on that resource increases. You're talking about what happens to the spend on resource A when the cost of resource B decreases. Whether it rises or falls, it won't be Jevons's paradox.