I've made Terry's base twice now, to the letter, using the Gold Madras. I really couldn't swear that it contributed anything special.
I've also used it as the curry powder constituent in the Bruce Edwards Spice Mix, and used that in my usual base and curries - once again, I couldn't register a difference from a BE spice mix using the TRS and Rajah Mild powders. The smell of the Rajah Mild and Gold powders in the packet, and their raw tastes on the tongue, are very similar - nothing jumps out at me.
If there is anything to be gained by using it, it must be very subtle. Certainly not a "crikey, this is what's been missing" type of difference.
Blimey, I sound like an old grump! I don't mean to.

I did mail Terry to ask if he knew what the ingredients of Rajah Madras Gold were, when I asked him for a sample. Although he kindly sent the sample, I didn't hear from him about the ingredients. I can't find them on the net, I'm afraid.
But I am toying with the idea of using what I've got left of it as a replacement for the spice mix in a madras dish, on its own. Just to see what it's like without being 'diluted' with the other spices.