Workshops as a whole provide income to whomever controls the workshop, be it an NPC or the player. With that said, they are extremely valuable for a number reasons the least of them being income. I'm not going to go into it all so I will cut to the chase.
I believe that when you go to purchase a workshop that there needs to be a few more balances before the NPC will do so. As it is now, all you require is a positive relation and a set amount of gold, and truth be told i'm not even sure if the relationship is required. I believe if an NPC is going to give up something so valuable that you need a higher reputation for it to even become an option. Say, 20 - 30 relationship before he will even discuss selling you anything in the town. There's already a check in the game for purchasing a troops, if you have negative relations they won't sell to you. Why not make it for workshops as well? This gives people a reason for keeping their relationships at a decent condition if they plan on expanding into getting workshops.
I believe that when you go to purchase a workshop that there needs to be a few more balances before the NPC will do so. As it is now, all you require is a positive relation and a set amount of gold, and truth be told i'm not even sure if the relationship is required. I believe if an NPC is going to give up something so valuable that you need a higher reputation for it to even become an option. Say, 20 - 30 relationship before he will even discuss selling you anything in the town. There's already a check in the game for purchasing a troops, if you have negative relations they won't sell to you. Why not make it for workshops as well? This gives people a reason for keeping their relationships at a decent condition if they plan on expanding into getting workshops.