WARNING: Incoming Wall of text. skip to the last paragraph for what I think could improve the gameplay experience. also, Momotarou question 2 blocks of text above the last paragraph.
This game has the Diablo element of farming for loots/resource and old school character stat customization. I have fun killing for loots and gold. However, unlike diablo(D3:RoS mostly), gaining resource in this game(mostly the in-game gold) is so hard to keep when you're trying to maximize your character through smelting. Smelting a higher level weapon(and high rarity rating) is such a huge resource drain because the price is titanic compared to the amount of gold you could gain.
***Example: smelting a blue rarity level 24 weapon cost ~55k gold at base, add to that skill evolution option alone and it goes up to ~158k adding a grade +3 grade is additional ~35k for total almost 200k. -- this is only for breaking the +10 limit.
***with similar smelt options(skill evolution and either grade+3/smelt success+5%) for breaking the +40 limit of the same weapon would be a roughly ~350k. so from +10 to +50 with skill evolution V option, this lv24 blue rarity weapon will cost total of atleast 700k-850k(without failing). and you're only gaining less than 20k gold per run on a lvl 31 dungeon. The grind is real. I could only assume The cost of smelting even higher level and rarity weapon would be exponentially higher and the money gain for the dungeon you need to run is still be lower, by a huge margin, than what you need.
The weapons you get are always Unidentified and the cost for identifying these are quite high that you'd spend 60%-80% of your gold you gained on the run to ID them all. and when you do ID them they sell for alot less than the ID cost you spent. and when they are not ID'd they sell for chump change that you can't even buy 1 potion with them.
I would not need to spend that much on smelting for skill evolution smelt option if Momotarou is useful. so far I haven't had the option of evolving any skill with him even if I maxed the level of that skill. so I cannot comment on Momotarou's gold drain since I haven't been able to use him because I simply couldn't. if someone knows why he wouldn't evolve my skills that are already maxed level, please let me know.
I don't care if they do not add Trading or auction house because usually, gold spammers will just ruin the economy just like they did in most farming mmo games like D3. I'd rather have this game tweaked where players get the most fun rather than balancing the resource gain around Trading/Auction house. I enjoyed farming D3:RoS because they no longer balanced the game through the auction house/trading but balanced the item/gold drops around what is fun for gameplay.
I Suggest the following to improve gameplay experience in the resource aspect: Reduce the difference between gaining gold and spending gold by balancing through the combination of the following: increase gold gain from drops, decrease smelting cost, decrease Identify cost, Increase gold amount of selling weapons, and Increase gold amount of selling trash miscellaneous items. repeatable kill quests for dungeons that reward gold and bag of random crafting materials for weapon/magatama/other crafting.