Display MoreMaking leveling up harder is a good idea.
Also i would like to suggest:
-when you inside a party in a dungeon if it's full then you get a passive buff maybe an exp boost, drop rate boost or stat boost by 5-10% for example.
-make exp harder to get from mobs in environment(outside dungeons) to make game more fun and challenging. That would make people farm EXP in a full party in a dungeon to level up making the game more Co-op based not solo leveling.
-in dungeons make a new currency that you get from there but inside a full party only. For example we call it Kiri fragments.
That currency you can exchange for items from a NPC outside each dungeon. These items depend on the level cap of the dungeon.
-Make dogis can be dismantled, you get dogi fragments that you can craft a new dogi with it. Add the dogis recipe NPC in kokkara.
i do like your suggestion about full party exp + lower xp rate slightly and item drop rate like 50% lower. +vipe with some gifts for founders and gifts for ppl who spend money, (lvlUp30 stone, cool vehistle, dogi of the choice, Z32 inventories some zeni BUT NO WEAPONS OR ARMORS, NO XP BOOST, nothing to crazy but more money you spend, more rewards you can get).