We all know that buffing your own buildings can take ages and that buffing a friend's buildings can take even longer.
After every buff the request is sent to the server, confirmed and then returned before the building shows any effects.
To speed this up, perhaps consideration could be given to making 'buff lists':
Allow each player to define one or more sets of up to 25 buildings.
Allow those sets to be editable by the player.
Allow the player (or any visiting friend) to buff an entire set with as many buffs as they choose.
Clicking the [Add / Remove Buildings] button would then return to island map, flag current buildings on the list and allow the player to remove a flag (with a click) or add a new building/flag by clicking any un-flagged building. Like buffing there would be a standard cancel button to exit the list management phase.
Adding a set of buffs to the desired list would be done by dropping a stack (or as many as you had) on the Mayor's House and then selecting which list to apply it to.
Shows 18/23 as 5 buildings are already buffed - the 2 zZz asleep buildings would still be counted though. Presumably small buff stacks (e.g. 6 irmas) would just target the first N buildings in the list.
Visiting friends would do exactly the same.
One click, one call to the server, job done.
Obviously thought would need to be given to the implementation, whether to incorporate it into the Economy Overview as conceptualized in the image or somewhere else, whether to charge gems for more than one set, whether to allow specialist buffs to be used etc etc