I started flipping through George's Progress and Poverty last night, and I was extremely impressed by his thinking in terms of scoping the problem.
There were a couple of things that caught my eye, and here they are. First, George seemed to consider speculative land bubbles as a means to increasing rents, not necessarily as an end in and of itself. Second, George did, in fact, lump speculative gains from the sale of inflated assets as part of rents. I realize this at least partly undercuts my first observation, but it does not do so where it counts. His focus was where the classical economists put it, which was on the marginal value of production (i.e., whatever is left after labor works capital to produce something, and capital pays the rent). When you frame the inquiry that way, of course speculative gains are completely overlooked.
Remember, though, I gleaned this from a very quick scan of certain sections of the book.
Still, my intiution is that George would have been better served to expand classical economics' labor-capital-rents paradigm to include a separate category for winnings instead of trying to redefine the term "rents," which neoclassical economics ultimately disappeared, thus extinguishing his argument. This explains the deep problems I have with starting a debate within somebody else's framework, particularly when that framework appears to be built upon layer after layer of lies and obsfucation. The person who chooses the battlefield most often wins the battle. Framing matters.