If you want to keep improving the 3D engine, I think frame rate is already good enough for a turn based game, maybe it would be better to focus on adding more lightning effects or something like that while keeping the same or similar frame rate.
I understand that you want to avoid levelling, but in that case maybe it would have been better to add some/more chests, besides increasing loot drop chance. I killed way more than ten enemies and they didn't drop any crystal, and thanks to the bosses bug they didn't give me their weapons, so stat wise I was like at the beginning of the game.
I'm happy you want to keep working on this game.
A GBA commercial game similar to yours that I like a lot is Mazes of Fate, you should try it if you haven't yet.