Thanks CFHM! There are indeed more upgrades later :) the later levels introduce new enemies and by the end you're melting those little 'space bats' that harangue you at the start. Also this progression is where I paid lip service to implemented the theme.
As I feel the controls may be a game breaking issue for those that hate tank controls, I quickly threw together a more modern system (copy paste of the enemy follow logic). It can be toggled by pressing 'M' in game.
Thank you so much for the feedback and hope to keep in touch.