The other thing to remember here is that there's so much diversity in the secondary market, it's probably pretty rare any of us are actually competing. Unless all you do is buy cheap and sell the next day, odds are your method is unique enough in time and place that never your paths shall meet. For example, let's count all the ways to sell a Funhouse. I can sell each figure. I can sell one lot of heroes and one of villains. I can sell all the figs plus the batcycle. I can sell the funhouse with no figs. I can sell the bricks in lots sorted by colors, then the manual, then the stickers, then the box. I can auction the sealed set starting at .99 or I can BIN at 45, 50, 60. I can flip it right now, or I can hold it until eol. After eol on a set, the Lego market seems to dictate that supply is irrelevant. As long as the set is popular (not a dud), the demand is there.
Edit: of course, all this is possible because Lego controls the supply from the manufacturing end of things. And with supply limits come purchase limits. I for one am glad Lego is proactive in this regard. A tighter primary market should mean a tighter secondary market, which means fewer sales for the same profits for all of us.