Yeah Maidame Curie is the true way of getting Coins But if you are at high enough level or stats to beat Gold Region final area enemies with ease they give up to 15m gold (with Gold Orb x3) and that's the way I'm currently using for weapon level maxing.
my current strategy is metal region 300 area and steal and crit high also I have attack all on my big hitter I got 50 experience trunks from block or jars can't remember which but been poping them and leveling like 3 to 7 levels a fight
Oh by the way if you get a few of the maid orbs get accelerators and just use them on the head then buy ability seeds you can get great stats really fast. Oh also how does gold help you level weapon upgrades? Do you just by a crap ton of the base stuff and throw it at it? Also right now I am rocking a purple garden sword+78 with good stats on it. Is besides the really late game stuff should I be grinding somewhere for better weapons?
It's not worth it leveling up equipment unless they have 200+ Base Attack (but it's best to wait with leveling up weapons until you find Azure Equipment which is the best possible ones.)
I made a short guide to weapon leveling up with gold and it requires a good flow of gold but it'll make maxing weapons far more efficient than stealing.
I said all possibilities that Gold offers as well as provided link to Gold Farming Guide. But that's best done post-game because weapons are best used for their effects (I see Steal 100% + Critical Rate 100% as good things.. But stealing weapons is less efficient way and requires hours of farming to get +100 in weapon for specific character. It's very useful when you're aiming for specific effects on weapons.
Critical 100 is the thing you should always have at any weapon because then any Skill used guarantees critical damage (at least I never saw not critical hit at 100% Critical Rate).
Maidame Curie is the true way of getting Coins 