Cool! It's always interesting to hear some of the longer use cases on the blankets I've made over the years. $75 for 15 years of use so far isn't too bad at all. Probably should have left a loose seam that could have got you coming back a little sooner.
99% of the parts you're covering on a diesel are thick castings, (manifolds, turbine housings, etc.) The stuff that isn't, hotpipes, up-pipes, etc. generally doesn't see much in the way of moisture due to their location in the engine bay. So my question is, how big of a concern is corrosion or the catastrophic hot oil spray scenario? Not usually enough to offset the premium price for Inconel/Stainless shields in most of the cases I've worked with.
Each situation is different though, I generally wouldn't expect an Inconel/Stainless heat shield to outperform a thick blanket in terms of heat control, as most I've seen don't contain a dense insulation layer but the benefit of corrosion and oil concern may be worth the trade-off in certain instances.
I can only really share what I've seen over the past 17 years and corrosion hasn't been something reported back with any frequency, especially in the diesel community.
If your blankets have lasted 15 years so far, how much more of a lifetime do you want or really need in a product and would it really be worth the additional moolah? A lot of this aerospace material stuff is just solid marketing without the benefit in my experience.