It's been a while since I've posted as life has gotten busy, however, this year has definitely been an eye opener for someone like me jumping back in the game after being out of it 9 years.
I think the Death Star remake definitely had the biggest impact, completely sucking the wind out of many reseller's sails. The idea that you could potentially buy a set at a premium only to have it rereleased in a couple months to a year was completely and totally devastating to me as a collector and reseller. I have stopped buying sets at post market prices because of this, and I am betting many other collector's have as well.
Tied for second would be the clones and just market saturation/lego fatigue. As someone who recently was buying sets at post market prices, I have since noticed that the sets I was buying from Jan. - May of this year have now since dropped in price. For example, I was watching the SSD like a hawk looking for a decent deal on it early this year. I felt LUCKY to buy one brand new in box for $800 dollars, and that was stalking eBay's Buy It Now Newly Listed listings. Now it is extremely easy to buy one at $800 an can be found for less. A set selling at $1,000 is difficult to move, whereas before it was standard. This is one example of either the clone effect or the Death Star Remake, or saturation. It's hard to say, but the bottom line is the set has decreased 20% in price since the beginning of the year and most of this drop has been since the release of the clone SSD. Whether coincidence or not, it is a real drop with timing that coincides with the lepin releases of SSD, DSII, 10179, etc. This is quite concerning for a flagship level set such as the SSD.
2017 will definitely be interesting from an investment perspective. In 2016 the market has changed more than ever before, and 2017 could be even rockier.