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.
Excellent news--especially because I would much rather have minifigs and a minifig-scale theme (NinjaGo) be responsible for LEGO's financial health than Bionicles--not least because Bionicle as such no longer exists.
Serious, I am glad to hear both that Lego has done well adn that they understadn the value of the smaller items in getting my money on a more regular basis. I will by a $69 to $99 set once a year or so for Birthday or Christmas. But I will buy a few $3.99 to $9.99 sets a month as the opportunity comes up. They have a better chance to get my money with the smaller sets and collectable minifigs.