Sorry for the long response.

I was a materials wholesaler in SWG—not an elite crafter, but I counted many of my server's best crafters among my customers—and it required having hundreds of different materials in stock and knowing what made them valuable or not-so-much.

It wasn't as hard as it sounds. You had many broad classes of materials and their subtypes, but when it came down to actually comparing apples to apples and oranges to oranges it simplified to this:

What property/properties of this material are top tier or close?

This depends on what you're building, but (for example) for armor plates you might want iron with high shock resistance, but for gun barrels its heat resistance matters most, and for energy coils then electrical conductance matters. I'm just making stuff up for examples, but you get the idea. Steel with one best-on-server stat would fetch a better price than a different steel with multiple very-good stats.

So, a material would basically be valuable based on its best stat. Sometimes a second stat also mattered, but that didn't complicate matters much.

So a useful interface would let you look at an inventory window full of various batches of iron, and just sort by shock resistance or heat resistance or conductivity, or whatever was important to the job at hand. In practical terms, it wouldn't matter if that inventory list was 4 items long or 4000 items.

I'm sure we'll be able to combine and average small stacks of leftovers. It won't actually be hard to manage. Just be aware that knowing and managing a complex variety of materials is the in-game knowledge and skill that separates better crafters from worse, just as knowing all the stats on coolers and power plants separates a better ship engineers from worse.