That seems like a great idea, but I don't think IMDb is going to cooperate with us. Yes, it should be an effective way to eliminate the regular "star" cast members. But the episode credits are still going to include any minor credits as well as the guest "stars." It's difficult to tell, but looking at a few cases, it looks like the results might be something like this: If credits downloaded are limited to "main page," there would normally be 15 of those. I done know how they determine who gets listed on the series page, but it appears the number that match those in the episode list might be something like five. That leaves 10 credits, of which only one or two would be considered "guest stars."
I think we need a site that consistently provides reliable "guest star" data. I haven't found one. The problem may be there is no standard way of specifying who is a "guest star." One studio may restrict it to what I would expect—the one or two "name" actors who make a one-time or occasional appearance. Another may include any "recurring regulars" who appear in an episode. And I suppose there's another issue—what's the difference between a "recurring regular" and a regular cast member?
I suppose I'm with darichman. I just want to know what Jessica Alba is in, so I can attach a hi-res photo. I was going to attach one here, but then I remembered—I'm the moderator!
