First, I want to say that I just started to play your game some days ago and I really love it ! It remembers me one of the Playstation 1 game named "Vandal Heart 1". You should really look at it and takes some good features in this game which is like similar to yours.
1st suggestion : in battle, you can find hidden item on a particular hex, your character has to use action like "hide" or "seek" while staying on this hex to find this item. It will add more interest into battle/strategy and not just win against the enemy team.
2nd suggestion : Increase team size by one for every world/area completed. It will be cool to win/add 1 more spot to our team once we reach a new world. It will add more diversity / difficulty to the game by increasing enemy team size too.
3rd suggestion : Add the possibility to upgrade "skin" of characters in our roster after reaching a certain level. Once you reach lvl 10 with one spearman, you can upgrade him in a special location (example : a church) and giving him a new skin with better stats
Hope you will find theses suggestions useful !