I think the blueprint is to expensive. We need them for going on to the promoted version of the construction and then pay 5000 enkord cash is unacceptable high. I had to buy now 3 of them in a week time.
If we pay in the next version monthly subscription, then you can not ask also for necessary items money
You do not have to use a blueprint on every upgrade, you can leave some at level 9, or destroy it and build the upgraded versions such as shrine to library, residence to town hall, they just take longer to build is all. You also can get blueprints in your towns lying around or fight monsters to get them, true rare but it can happen.