I guess I'll be the lone dissenter here -- I have both but I go back to the Classics more. Usually, I just do Step Heat because it's about an hour and it has an abs section as part of the workout. I find both DVDs to be at about the same level of intensity (but that's just me.). Based on...
I just bought gliding disks (carpet version) for $18.95 from FWOnline (http://www.fwonline.com/glides.htm). I'm not sure how well they work yet, though. I'm waiting for STS to start using them.
I recently stumbled across a product called Versa-Loops, which are like a resistance band but in loop form. I think these would be great for firewalkers! I've already put a hole in my resistance band trying to untie it :( I'd love to see Cathe sell a product like this. I'd buy one for sure.