Currently, almost nothing needs advanced circuitry. The electric jetpack, the terraformer and blueprints, the OV scanner, the nuclear reactor and some parts, the mining laser, the MFSU, and the matter fabricator->quantum armor series. The teleporter, notably, does not.
Let's read that again.
The TELEPORTER does not require any "advanced circuits".
Fucked up, right? That's clearly the most extreme offender, but far from the only one (Carbon Fibers->Nano Armor series, I'm looking at you). As a result, if we get the insulation option I asked for, damn-near everything on the tech tree with the--singular, I believe--exception of the Transformer Upgrade is accessible without rubber. So here's where you come in, with this excellent point about the uselessness of the most conductive metal on the planet:
1. Make Advanced Circuits dependent on gold, and not only by assuming people won't scour the Nether for glowstone. In fact, almost every recipe that includes glowstone dust shouldn't. It's a light-source, not a magical bauble. I can see the argument for leaving it in Teleporters, because it's specifically a trans-dimensional light source, but I'm veering rapidly off the topic, now. So. Gold should appear in Advanced Circuits, and not as dust. Gold Wires, arranged like the copper is in Basic Circuits
2. I do mean "Wires", not "Cables", because this is a tiny, delicate operation. Gold Cables, as they currently exist, are senseless. The metal is far too rare in real life to use in long-distance power grid applications, and trying to sensibly account for its comparative abundance in Minecraft just makes the cabling situation a nightmare to balance. As you've already mentioned, everyone jumps from Copper Cables to HV Cables already, so strike gold ones entirely. Instead of eating whatever O(n) problems the extra TileEntity entries cause, make Gold Wires just an item, produced by the same recipe that 1x Insulated Gold Cable currently is. Use it in Advanced Circuits and some other delicate things I'll mention later.
3. Then make an item that involves spooling a bunch of Gold Wires together to make a stouter cable--I'll call it Gold Cable for the sake of the discussion, but it needs a better name--and use that in more robust applications that still require higher currents. I'll get into them, but I'm trying to highlight one application per numeral. Next, the Gold Cable applications, then I get back to the Gold Wire-via-Advance Circuit applications.
___
4. HV Transformers, as you pointed out, should be using Gold Cables, not Copper Cables that really ought to be burning out, under IC's EU paradigm.
5. The Magnetizer is not a simple electromagnet, but some kind of crazy induction engine. It should be using Gold Cables, too. As an aside, there's not a single metal component in Nano Boots. They shouldn't work with the Magnetizer. Quantum Boots still could.
6. The MFEU should probably not be easily reachable with wool, and it outputs more EU/t than Copper Cables can carry, so it needs Gold Cables internally, too.
7. This would incidentally make operating the Electrolyzer dependent on gold, since it can't interface with a BatBox. This is intended.
___
8. And now for delicate integrated circuitry. First, the Solar Panel. Guys, these things are made by microprocessor-style doping techniques and connected with nano-scale circuitry. They ought to require Advanced Circuits, not Basic Circuits. Come on.
9. The Lapotron Crystal is supposed to be the most powerful and advanced portable energy storage device in existence, incapable of outputting less than 512EU/t, and it doesn't need any kind of complicated programming to operate? You gotta' be kidding me.
10. Let's keep the Crop-Matron at its current technology level, because it's useful for survival-level agriculture. But if you want to get into serious recombinant botany, you need the Cropnalyzer, and that's not a simple task. Make this require an Advanced Circuit, ergo Gold Wires, ergo gold, and now gold is the key to one of the most creative and entertaining elements of IndustrialCraft: beer.
11. The Teleporter does not currently require Advanced Circuits. In fact, it only requires two Basic Circuits. I can't comment any further on this without yelling.
12. Finally, the incredible heat output of the Induction Furnace should require at least a couple pieces of Iridium Plating (As mentioned in response to an Iridium-as-blast-resistance Suggestion, it's real application is as a heat-tolerance adulterant in making alloys.) to keep it from burning down its surroundings like a near-critical Nuclear Reactor. This makes it dependent on the Matter Fabricator, and therefore on Advanced Circuits. If it needs a further efficiency boost to justify the EU spent to make it, so be it, but I don't really think that's the case.
---
So there are twelve excellent ways to integrate gold back into Minecraft with the power of industrialization. I dare say they would, collectively, make most existing advanced operations gold-hungry and eager to find more of it. That's a GREAT thing, because it not only reasonable emulates gold's actual scarcity, it makes skipping the Nether and blowing through kilotons of Gold Dust to make Glowstone Dust a meaningful trade-off, not an obvious decision. What's more, I like it because it takes away my own biggest reservation about creating a non-rubber route to Insulated Copper Cables, that too much advanced technology would be go from bottlenecked by Rubber Trees to not needing them at all.
- with the mfsu set to emit if full
