Sorry bro, I personally disagree with the idea. Its good your sharing ideas as you will always come up with a good one, but in my opinion, buying sols at NPC will remove the thrill and challenge that the game gives us, that would also come up on losing the will and goal to own the castle for it is easy to obtain it. I believe it is the challenge and difficulty of the game that keeps us going, imagine a world where you can have everything you want, that would be boring right?
my opinion. Good suggestion though.