Well, I'm glad you appreciated my feedback.
I think I like the idea of scaling income with design because it encourages people to take on the more challenging designs, and also encourages people in investing more money into more features. (Rather than just having more pieces to play with. I know I avoided some purchases I would have liked just to simplify the process of farming money for advancing the plot.) On the other hand, it is nicely simple as it currently is too. If you tweaked the gold amount needed, that probably already helps plenty. :)
Looking forward to the following chapters.