Prices on second-hand games is always going to be a constantly fluctuating variable. You should always look to the basics of supply and demand. Supply, in the case of LRG, is a known and posted quantity. We essentially know exactly what the supply is for any and all of the truly "limited" titles they put out. The supply is less certain for their pre-order titles, as those supplies are dictated by the number of people lining up to purchase them, instead of being a fixed number ahead of time. Those figures can fluctuate from game to game, but we can still "ballpark" the limits of them.
Demand is where things get murky. Demand is far more nebulous, and far more contingent on various factors out of the control of the average person on the street. Attempting to predict demand requires far more consideration, and involves far more variables.
The long-term success of LRG has actually lowered the demand for their titles in the second-hand market. There would be considerably more demand for their games if they had gone out of business at some point. The fact that their business model has proven successful and stable means that there isn't going to be any immediate end to their products. While the print runs of their individual publications are inherently limited, the company itself and its continuing output has no expiration date. This lowers the immediate demand for their titles. You don't need to get as hyped when this has been going on for years, and likely will continue to for years to come. Mundanity lowers the demand.
The speculation bubble for LRG titles has also burst. The long-term viability of this business model has also taken the wind out of short-term speculation. Even the more hard-core collectors have realized that a bit of patience will allow them to pick up copies at reasonable prices. They are no longer frothing at the mouth to pay exorbitant prices for games they missed out on getting. And speculators in turn are starting to get burned by copies that don't immediately appreciate in value for fast flipping. The success of the pre-order entries have further worn down the practice of short-term flipping.
Bottom line, I will reiterate what I'm always harping on about. Short-term game speculation is a terrible idea, and you shouldn't engage with it. Game collecting and selling has a very long time investment. Games, even rare ones, take a while before they appreciate in re-sale value, and there are numerous factors that affect that sale value. Snatching up games out of a desire to make money off of re-selling them is a terrible waste of time and resources. You'd make way more money by just getting a regular job. "Flipping" games properly requires that you sit on a title for 30+ years. And even then you'd see better profits from so many other hobbies. Game collecting is not a good place for speculative investment.