It's so hard to upgrade something, everything is so expensive and you get less gold by attacking with 2000-2500 trophies than you do with 1000-1500. It really feels that the only way to get the lasts upgrades is buying gems; it should be a way to normal players to also get there.
There should be an option for players to choose between different upgrade costs. Being able to reduce costs if you are willing to wait longer. Example: Mortar upgrade level 8 for 6.4M for 10 days, 5.4M for 15 days and 4.4M for 20 days.