Hey all,
According to this article LEGO has seen a worldwide jump in sales by 25% for the first six months of 2011 compared to the first six months of 2010. They credit it to Ninjago and the Collectible figs - basically things that encourage kids (and us) to keep making small purchases rather than get one big set. So I think that assures the longevity of the Collectible line, and probably look for other things of this sort.
BTW, I was in a toy store a couple of weeks ago and saw that Playmo has a similar line of single-fig packages where you don't know what you'll get until you open it. The one difference is that they were divided into 'boy' and 'girl' packages.
Bruce