I agree that Elling's equipment discussions are dated, but the techniques he describes definitely are not. So, it's really more an issue of the accompanying photos looking very old-school.
I also agree that Warren Witherell's The Athletic Skier is a worthy addition.
And back on the subject of old-school, an irreplaceable addition to anyone's ski book library is Warren Witherell's How the Racers Ski, a timeless book on the essence of carving like a racer. I learned to carve in the early to mid 80s thanks to Witherell's book. It helped me get more out of my Dynamic VR27 SL Carbons.
I still want to read Ellen Post Foster's book on carving.
Lisa Feinberg Densmore wrote a good book on racing technique, fitness and stragegy, but I forget the name. I read most of it one rainy day at my local Barnes & Noble.