Once you finish off Broken Valley (specifically Maxos Temple) you will gain access to sentinel island, where (after some exploring and quests) you will be able to take over the battle tower there and become a full dragon knight. The servants / runners come with the battle tower; once fully upgraded you can use them to gather gems/minerals to use in enchantments or sell (malachite ore and diamonds being the most expensive), so 'wasting' 500 gold isn't a big deal.
