I am getting close to finishing a PhD in applied math (next May), and I'm starting to think about job applications next fall. I taught for 5 years as a GTA (graduate teaching assistant), but I still feel like my teaching portfolio could use a boost since the last 2 years of my degree I was funded on a research grant. One idea I cooked up was to create and publish a series of Khan-academy style "screen-cast" lectures on various interesting topics in mathematics. Since this could potentially consume a fair amount of time, I'm wondering what the benefit of it would actually be for an application to say, a teaching post-doc or tenure track at a SLAC (selective liberal arts college) or (not R1) public university. Obviously if they're good, it demonstrates an ability to clearly organize and present material, but would anyone actually look at them if they saw it on a CV or in a teaching statement?
I would advise against doing this, even without knowledge of tghe hiring processes in SLACs (never heard about those before) or the universities you're interested in.
On principle, it does not make sense to have projects in life whose main or only purpose is make your CV look better. If you're passionate enough about this to do it for its own sake - say, because you feel available material is not engaging enough and you had good feedback from your students - then maybe it could be a reasonable use of your time. Otherwise, your days are better doing proper research, or other publicly-visible math-related projects which are of interest to you.
Also, if you got good feedback on your teaching, I doubt your focus on research will be held against you, especially since you do have a solid 3 years. Perhaps some letter of recommendation from professors/lecturers who were in charge of the courses in which you taught could serve as guarantee of your capabilities.