After thinking about it, the proposed NPCs are simply to be lazy. Healer, is helpful due to the fact you'd have to wait to heal normally, or use items to heal. An NPC to sell stuff you get from the missions is just being lazy as you don't want to warp to town, sell, and then come back. For that option, you can simply drop items on the ground. As for repairman, there are repair weapon scrolls available in the game and you can always just bring a blacksmith along with you. I mean, who doesn't use alts in these quests? >.>
Strongly leading on No for this, but feel free to debate how it's not a "I don't want to walk to town and back" idea.
As the topic starter, I fully understand your decision of saying No to this even though the topic is still open for debate and comments. It is merely a suggestion of mine. Seeing as how we can be easily walk right into Prontera Castle, I understand and i get the point now. Guild Towns are open to some (if not, most) and there's also the option of warping to Valkyrie Realm and go down onto Prontera Castle. Do what you must and what you think is best, GM. Thanks for opening the topic.
I rest my case now.