From my understanding of the proposed upgrade costs, for most players this will require a phenomenal investment of time and/or effort in order to achieve any upgrades, or else put it out of reach entirely. Seeing as how literally everyone was severely negatively affected by The Great Building Nerf, it seems the vast majority will be much worse off with this feature, than if Inno had chosen to do nothing at all. I do like the idea of being able to upgrade event buildings, but I think the cost to do so needs to be rethought, and/or increase the number we can get in game, such as earning more in tournaments, or enabling us to craft the spell.
Using the Spheric stub for an example calculation:
This is a 4x4 building, and at a proposed cost of 1 spell per tile, this will therefore cost 16 spells to upgrade a mere 1 level.
A player who is reasonably small, or in a reasonably low level fellowship, will achieve 1 spell in the 3rd chest (if they can get this far), and therefore take 16 weeks (at least) to save up enough spells to upgrade it 1 level.
A medium sized player/fellowship that consistently completes 5 chests will get 3 spells in a tournament and therefore take the equivalent of 5.3 weeks to upgrade it 1 level, which is still a lot.
The largest players in fellowships who invest heavily in tournaments and reach the 10th chest will get 11 spells per tournament, and take the equivalent of 1.5 weeks to save up enough spells to upgrade it 1 level.
Now consider: how many buildings did you have nerfed? How many levels will you need to upgrade them all to something akin to what they were? Or even just to the point where they're worthwhile. How many tiles do they all take up? So just how many spells will you need? And how much time and resources will you need to invest just to get that from tournaments?
For many, even those who aren't anything close to large players, we could be looking at something like hundreds, maybe even thousands of spells needed just to undo the damage of The Great Building Nerf. This is unviable, so either the upgrade cost must come down, or we need to be able to get more spells in game without investing a ridiculous amount of time or resources. Preferably both.
*Post edited to adjust calculation numbers, as they are now known.*