You misunderstood what I was saying.
"Too complicated" referred to splitting the topic without disrupting the on-topic conversation. I wasn't saying anything about IOR there.
Metals (conductors) need to be handled differently from other materials. Metals/conductors need to either use a metalness parameter or a separate underlying layer with high IOR to mimic their high reflectivity.
Most non-metals are dielectrics. With dielectrics I maintain that you can use real world IOR values in Terragen. Where confusion arises is with roughness. An IOR of 1.5 doesn't make it shiny if the roughness is high enough. If you have a material that looks too shiny when you plug in a real-world IOR, this is a very strong hint that you need to change the roughness.
IOR values in the real world correspond to settings in Terragen. IOR tables can and should be used, there are just some caveats to consider. This is a really useful tool to help make your materials mor realistic. When someone discovers this they make a leap in understanding. That's why I think care should be taken when starting a reply with a broad statement like "TG index of refraction values do not match scientific values at all FYI. Waaaay off from scanned readings for many materials, most especially being reflective." That's why I said you were generalizing. I don't want people to read that and start thinking that IOR values can't be used, because they can and they should be used. Discussion should focus on the exceptions to this rule, and how to handle those exceptions.
In Terragen 4.5 the Default Shader will have a metalness parameter. When you set this to 1, the base colour is used for the reflective colour of the metal. IOR values affect the transition towards glancing angles, so they are still important, but you don't need to cheat with high values anymore.
In versions prior to 4.5, I recommend mixing a normal IOR top layer with an underlying fake IOR for metals.
For non-metals, the primary way to control how shiny they are is the roughness parameter.
Of course these are just approximations of reality, and small tweaks may be needed. But if you find that IOR is "way off" for a dielectric and it can't be fixed with roughness, the next things to look at should be lighting, environment and render methods.