Mica Goldstone
Items were designed using two basic premises.

1. If it is a direct improvement on an existing item it has the same name and a higher mk. In these cases the item requires higher levels of technology and more often than not, rarer minerals.
In these cases there will be a progression of item power as the mk increases. The progression will invariably be exponentially decreasing while the build requirements will increase, i.e. follows the law of diminishing returns.

2. If an item duplicates a similar technology but is based on different principles it will have a different name and will require different raw materials.
In these cases the use of exotic minerals may allow an item to duplicate a much more technologically advanced item that only requires uncommon ores and vice versa.
Stealth plates are a classic example of this type of technology. They perform in exactly the same manner as korondite plates for the purposes of sensor profile. They are however technologically more advanced. This advancement is reflected in the use of common minerals instead of the uncommon mineral korondite.

So, basically speaking the incorporation of exotic ores within an item allows scientists to circumvent technological problems that science simply has not found a way of solving. Where this is the case though there are usually other drawbacks such as fragility, size etc.

The above are guidelines and game designers rules of thumb. They are not set in stone and no, a lump of unique ore cannot be turned into a fananabananasuperduperuber blaster simply because it is unique.