The videos are there to help get started, and point out some tricks and tips that are not readily apparent. You also should take the ideas and adapt them along.
Taking a close look at your pictures, there are a number of ways you can tackle it, some of the methods are derived out of Cereal's techniques, others are from experimenting.
The curved region is divided into three sections from what I can see.. The most raised surface that serves as the temple, The circular ear cup, and the little recessed area between the first two.
If you want to smooth it well, I would probably take masking tape and cut it to fit on the floor of the recessed area. Then press bondo against the "cliff" between the temple plate and the recessed area. When the bondo is half dry you would pull the tape up to cut the bondo into a smoother curve. Then use an exacto knife to clean it up a bit while it is still pliable. Finally, when it's dry you would take a piece of mid grit sandpaper and hold it against your fingertip to sand down that cliff, or get a good diamond file (they make curved ones that could be useful).
I used a similar technique to raise and sharpen the edge on my ODST visor buck:
To smooth the floor of the recessed area, you would do the opposite, and tape off the cliff and the earcup, then carefully use a cut popsicle stick or chopstick with a flat head and smooth bondo over it, peel the tape to cut it and then sand it with sandpaper on your fingertip, or a flat headed file.
Spot putty is great, but it does not get the grip strength needed over a large area, so be wary about applying it as a filler of anything larger than a couple millimeters. Someone once mentioned possibly using spot putty to completely replace bondo, but it suffers from major chalking, cracking, and lack of grip strength on large areas and the idea was ditched after failed attempts. Definitely a staple of my pepakura kit though, as it is fantastic for getting a high quality smooth and filling the little bubble holes in bondo. It'd be interesting to see how it would perform on the recessed curve in the iron man helmet.