Figures are ultimately depreciating assets, and further 95% of all figures will see price drops on the secondhand market within just a few months of their release. However, I preorder my share of items and my take is that when I preorder, I'm paying a premium for some combination of convenience and immediate gratification.
Reliably predicting outliers (in this case the 5% of figures that will see price increases post-release) is of course a tricky/impossible business but there are a few heuristics I use.
I'll keep an eye on the MFC statistics for the item (ordered/wished numbers), and figures from the bigger manufacturers (Koto, GSC, ...) with low preorder numbers might be a signal that the figure will hit the bargain bin. Conversely, figures from more niche companies with low preorder numbers are better candidates for preorder since there's a higher probability that those items will be scarce on the secondary market. The way I see it, a company like Q-Six is going to be a lot more conservative with their production runs than a company like Good Smile.
Where things get really tricky is when the preorder numbers are high. Then the question is whether that's signaling a future glut of pre-owned supply or some truly exceptional item that's going to disappear into peoples' collections and be in short supply. Then, it's time to roll the dice, make a decision, and hope for the best...