The value of the Lethicite Staff is internet slang for "Leet", meaning "elite".
The Lethicite Staff shares its perk with the other staffs of the game. However, it provides the biggest increase to spell power-- the next in line is the Eldritch Staff, with a 60% increase.
The Lethicite Staff became unavailable after the CoC Mod's version of Lethice was replaced with the official release of her, as the official Lethice doesn't drop a Lethicite Staff. Being able to craft it was eventually done by Foxwells, making it obtainable again.
Weapons are equippable items used to boost attack, among other effects.