Just wanted everybody’s views on this.
I suggest an improvement.
Most of us do not know the maximum levels of units and spells. Either we ask each other or check on the net. Wouldn’t it be nice if the details were provided in-game?
What I suggest is, when we (eg. spell) select a spell to upgrade there is a window, which opens up giving details of the next upgrade (it is nice). A slight improvement to this can be that a thermometer like a Bar chart or something can be shown in the same window that shows the current level (where we are) and the other levels to reach the maximum with the gold needed.
This will also help the player to be motivated to achieve the max. level.
The same applies to the units, towers, etc. as well.