If you see a figure and you instantly know you want it and will get it, definitely pre-order it. Had the tragic mistake of not pre-ordering item #396850 (granted I hadn't read or watched BSD until a few days after pre-orders closed, but I still loved his character design immediately) and then the price shot up to nothing below $90. Got lucky since GSD decided to re-release them for September, so I learned from my mistake and also pre-ordered Chuuya as well, just in case.
Basically, if you love a figure, it's usually not worth risking the chance of it having an insane after-market price. Like, I love Dazai and all, but I'm not paying $100+ for his nendoroid xP