I feel like posting here will be jumping into a can of worms, and I haven't read everything about this topic yet, so please take what I say with a grain of salt.
I've been playing for 4 years. I have not figured out combat to the point that I have enough units to do world map, tournament and spire completely. At this point, I explore only to fulfill quest requirements, nothing more. I do 27 to 36 provinces per tournament, give or take a few. And I try to do the first level of the spire, sometimes I don't make it, sometimes I make it a little farther. Then I run out of resources and units. Do I know that it is possible to do more? Sure, some of my FS members do it and many of you do it, so it is possible - and possible without spending money on diamonds.
Even so, I am always running short on spell fragments, and when I started chapter 18, I was desperately in need of mana, so I took the four moonstone libraries that I had been saving in my inventory from many chapters ago, plus several of the other associated buildings and placed them for maximum yield. And I have spent hundreds of RRs on bringing the mana plants and library buildings up to my current level. Still haven't got there with the libraries, I might add.
That being said, (and I don't want to lose my Moonstone campus), maybe the best location for the Moonstone Library set is the Magic Academy, just like the chess set. This lets you get all of the pieces once, and then replace them each chapter by deleting them and crafting them again, without having to chance maybe getting them in the spire and, if you think that people shouldn't have many copies (like I do), that won't happen. It would also save the cost of all the RRs to upgrade them from previous chapters (oiy.)
I don't think that we need more buildings that produce spell fragments. I like the moonstone library. If necessary, modify the library to improve(correct?) it's yield to what you want it to do, but why make something else when you already have something? People can also get spell fragments from disenchanting summonings and spells. If people need more resources for spell fragments (and I will admit that I do), how about if we were able to recover spell fragments every time we delete a building from the city map? Should only be for event buildings, of course. Otherwise people will build buildings just to delete them.