FigmentValley is on point. Increased chances may not necessarily be obvious or even realized with a small sample of breedings. I can't possibly do 30 breeds in a matter of a few days like Anyuszko has reported. So those of us who are not willing or able to spend gold to rush our dens and nests will fall into the category of "small sample." I myself was one of the lucky ones who saw Common results from Boosted Breed during this special event.
But I won't complain too much because Vampire came out of my NON-boosted den this weekend (Metal-Night), and Darksteel was produced with boost last night. No such joy since. The Lotus-Night boosted breed is making Water. Yah.