What is the point of the enriched iron/copper/rare metal processing recipes?

Okay, they save about 25% ore, but they cost around the same in sulphuric acid, so it's not really a saving.

I'm not sure what to suggest; they're simply a complex way of doing nothing useful?

I don't think you actually did the numbers ... the cost of the sulfuric acid is pretty much negligible.

With prod 3 modules the productivity increase is about 86.57%.

I compared the two processes with helmod. Ignore the energy consumption and factory count, I just used prod 3, no other modules or beacons. Just focus on the material cost.
Here is what I got:

Normal process:

Enriched process:

I used matter as a source for the oil just to give you a comparison of how much the oil is worth in iron ore.

And in your case the acid is around half the amount of oil; without modules it's about 1.5 times the amount of oil. Okay, sounds like this is only really worthwhile with prod modules... although normally ores are so cheap that it hardly matters even then. Thanks.

Especially when you get the advanced chem plant with 4 module slots it's really worth it.

I think it should be more efficient/faster to smelt enriched ore. That's where the benefit should come in since saving on raw ore amounts doesn't matter. You can always expand to another location.

It doubles (if you convert dirt water) the number of plates you generate (with prod 3 modules) for the cost of some space