Yesterday evening I finished to maximize everything: all my units (except for ogre, gargoyle, mummy and werewolf), spells, towers, obstacles, farms, taverns, buildings, waves, alliance tower, conquest buildings are maxed (in the case of blacksmith slots it’s better to say all unlocked).
Then I can say congrats, you finished all gem costing stuff. That’s a milestone. I wait for a discount on conquest buildings to max 2 out of 3. I still need to get around 2.5k gems to max them all during discount.
Next goal is completing all dungeons, for that join a team with boosts strong enough. I did finish them all, when our team was below level 50.
Don’t forget to forge everything you have a lot of times, it will improve them by 30-40%.