In many ways, however, I think Lego is somewhat immune from the worst of it. First, it's really not all that hard to find sets that are several years old. Secondly, you're going to have to hold on to that set for a very long time before you can hope to profit on it. I already see parents complaining about the price of Lego on a regular basis, so I can't imagine them spending double or more on an old set when there are dozens of new sets, the ones kids are going to want, are readily available.
This isn't like the Transformers Alternators craze from several back. Hasbro had a crap distribution channel, whether it was intentional or a consequence of corporate disorganization I don't know. What it meant that very few sets made it to the stores and those that did were promptly snapped up by vultures. At the time those were $20-$30 but because they were so hard to find you had people willing to pay double or triple the price. People started hoarding all Transformers, new and old and values skyrocketed. Then some guys got their hands on old molds and starting producing fairly good reproductions in China, all the way down to stickers and packaging. Then the bubble burst and everything went back to being more reasonably priced. To this day values haven't returned to their original heights.
Lego is too widely distributed for it to be a viable investment. The ability to build whatever you want negates the need to even hoard an old set and it's trivial to buy individual pieces. So I think whatever investing happens is going to be more focused, centered around minifig packs and stuff like that.