Each kal geons quest has a limited number of completions, and therefore theres a limit you can make from a particular kal online geons quest. However, each coin quest is simple, usually a kill-task. After you complete the quest, the NPC will grant you a nice kal gold bonus, plus, you will get nice kal gold from the thrash loot that you will get by completing the quest. XP here is pretty nice, the mobs have a juicy loot table and they also drop kal money. You will get here nice amounts of Abyss Points as well. Last spot Im going to show here, that this leveling guide has brought to my knowledge, is placed on the lower island, West from Lake Asteria. The mobs here are level 33-34 Undead type, and give excellent amounts of XP.
Therefore, here are a few of them: First spot Ive came across is situated North-East of Lake Asteria. The mobs good to grind on here are the Mirrorglass Worms. They can be easily soloed by any class, they dont deal too much damage, but its a good idea to come here at least at level 28, for a smooth grinding. The worms are pretty easy to kill and even the grey loot from them is quite valuable.