Imo inno is missing out on what could be a very nice revenue stream.
Premium skins.
Purely cosmetic purchases that alter the appearance of a building. Some of it wouldn't even require any new art-- for example allowing players to make a level 19 dust factory look like a level 18 dust factory.
Or taken a little further, and orc level 21 residence could look like a snowy charming tree.
Perhaps a premium spell could do it. Maybe you could also win them in the FA, or events.
There are loads of city builder games, and what really sets Elvenar apart from most is the beautiful art style, but some of it is totally wasted. Either it's only available for 1 event, or it's a middle building upgrade that you only see for a couple of minutes before you click upgrade again.