In general - don't expect too much. While the game is fun, from the structure so far getting any big improvements would require a major refactoring of even the core-concepts of the program.
Overall the performance, for what it does, is not good, but also not as terrible as most indie-games are.
I would expect than within the next year or so you can get maybe 1/3rd better performance? That#s around the level of improvement you can expect from better code-maturity.