Quote: What do all those additional features do for me?
One more wheel adds a little bit of control, and - this one I'm not sure about - enables hyper-program mode that Pentax is so proud of
So, when you're shooting program AE, you can turn front wheel to instantly change into Tv mode, or rear wheel to instantly change into Av mode; afterwards, pressing green button takes you back to program.
Also when reviewing pictures, you can use front wheel to change the picture without having to zoom all the way out - useful when you have two pictures of the same subject, and you want to see which one has better focus, per se.
Also, green button would be especially useful for you, since you're going to shoot manual lenses. Basically, you will have to use those lenses in camera's M mode, and you will use aperture ring to set the aperture, and then press green button so that camera can meter and select an appropriate shutter speed. That said, I would guess K100Ds has some sort of feature that does the same thing? Or, how else do so many people around here with older cameras shoot manual lenses?