As a preface I'd like to clarify what I mean under Unique items. It includes, besides one of a kind items, all items you can get through enemy drops, bought or found, but aren't craftable.
Now onto the topic at hand. Unique items, be it armor or weapons, while having their use, are usually outclassed even by normal gear a few levels later, and completely overshadowed by crafted items. Which makes uniques a more of a collector's thing to horde at your house and not utilize properly, exceptions being a few handful of items, like CAU armor, Regalia, Power Fist, Jackknife etc.
Giving a direct buff to uniques is a bit obtuse and may break the balance, but there are alternatives:
1)Utilize crafting skills with feat(s). A simple, yet effective method.
-At 90-100 skill points in either crafting skills (mechanic, tailoring, electronics) have a feat available called "Reverse Engineering" or "Artisan Craftsmanship". This feat may or may not require "Disassemble" as a prerequisite, as see fit. The feat enables a new crafting option with a large variety of slots to accommodate all types of uniques. By slotting in a unique item, the upgrade material is based off their normal item counterpart, e.g. shotguns use shotgun frames, armor uses plates etc. Each unique should have an approximate base Quality level and is depended relative to similar quality items when it is found. That base quality level is used to determine by how much the unique is upgraded (and which minimum level quality it needs).
Example: Salvation-12 (which I from now on will call SPAS-12) is a unique combat shotgun, therefore in the upgrade window it will require 3 combat shotgun frames of all different types: sovereign, despot, tyranny. The formula (a rough example) for added quality/stats is something like this (x+y+z)/3-SPAS-12Q. If the formula is correct then you don't go above the average quality of the upgrade component's sum. In addition to basic stat boosts, you can add other upgrades, such as extended mag or foregrip.
2)Have a master weaponsmith and armorer in Underrail, mainly in a location like Foundry or Core City. The process is similar to first example, only you give the item to the master and he/she upgrades it to the needed amount. It is an alternative to no-craft focused builds, even though it somewhat cheapens the usefulness of crafting, which is why the price for upgrading should be high and time consuming. Not just charons and a time wait. Maybe a specific item needs to be found, and each unique item has it's own. Some people have suggested to get a unique frame from disassembly, but since frames are the ones deciding the damage, and can't be upgradable in the base game, here, they have merit, as the frames can be upgraded to a higher quality and later used in personal crafting.
3)The most simple version, a basic upgrade workbench. You put the item in, give it money/upgrade blueprint/data etc. and receive an upgraded item. No crafting skills required, only getting the bench, money and data.
The result of whatever option is chosen is a unique weapon or armor that can be utilized on par with crafted items and not become irrelevant 2 levels later, while still retaining it's unique nature. AKA becoming viable and possibly used in meta.
Certain uniques can even have a unique upgrade, like the H&K MP5 with a silencer can become an H&K MP5SD with a corresponding model/icon.
