About your weapon refine I have an idea (a bit ripped from Ragnarok but nevermind xD). With your enchaniting system you have the same % to make your weapon better for ex. orcish axe and thunder hammer.
What i mean? You can make class for weapon for example A,B,C,D and items like orcish axe are in D class coz its useless item, thunder hammer goes to 'A' for sure. Then a percent% chance for upgrading orcish axe can be a lot better then upgrading thunder hammer (its only example)
look here to understand it better:
Weapon and Armor Refine Success Rates - Ragnarok Online
I dont mean exactly the same system I'm giving an example to make it more balanced/complicated xD