A large reason why it is beneficial is the decreased under hood temperatures and not the fact it helps retain heat energy in the exhaust gasses. This is the same reason the stock precats and Y-pipe are clamshell shielded. There is less heat transfer to the engine bay & oil pan.
That site was mainly for using coatings over wrap. There is no argument there because a quality coating is superior to a wrap in longevity of itself and the piece in question.
Now the durability of aluminized steel far surpasses what most people give it credit for. Metallurgy has come a long way. My headers are 4 years old. From the collectors back have been wrapped for over 3 of those years. My Y-pipe/down pipes have also been wrapped for 3+ years. First as a Y-pipe and then as part of my duals a year later. None show any significant degradation. Yes the headers have a basic ceramic coating. Yes I sprayed everything with Thermo-Tec when I did my 3L. (over 2 years ago now) I did not wrap the primaries for concerns of over stressing the metal.
The important part is that you can touch the wrap even after spirited driving. Regardless of the extra stress on the metal the fact that exhaust heat is not entering the oil pan and engine bay are worth it to me. I will let everyone know when I have to build another set of down pipes.
