Upgrading the enemy is a fun idea.
When first starting... click and move isn't satisfying. I wanted to click a bunch to move faster. I think if there was a reason you can only click once per second that would be better. A progress bar or make it a creature like a tadpole that is doing a breast stroke.
Getting hit doesn't have any effect. Maybe a health bar that goes down would help? Or you lose money each time you are hit? I can see how getting hit is in conflit with the idea of an idle game that you can walk away from.
It gets pretty easy staying as far away as possible. Maybe the level gets smaller and bigger over time?
Bullet hell is fun and helps fix the difficulty level.
Great work!