Some items, such as engines and spaceship, can have normal, uncommon, rare and legendary rarity. This is, unfortunately , limited to these items. I could suggest extending this to weapons as well. With rarity attached, the weapon can have an improve machanic like more damage or faster projectile speed. Some can even have spread or condense fire-patterns.THis exist as mountables but this could allow or wider spreads to be obtained if , let say, the neuton gun is uncommon and has a bonus mechanic of spread.Along with this, attaching spread mountables, this can cause the projectiles to spread out more than the regular neutron gun with spread mountable.
Note:The mechanics should provide a small boost. An example could be 5% projectile spread increase. Also it should counterbalance to ensure the weapon become unbalance. Continuing with the example previously mention, there could be a 2% firerate reduction.
This idea has many possiblities. Comment below if you agree or not and state your opinion( whatever it may be).