I know it's "just a small project" but it looks really good! It's pretty much Nodebuster but without the glow lol.
About that "hitting multiple enemies at the same time" thing. I noticed that when you shoot 2 enemies at once, you take the damage of both of them. This mechanic, paired with the increase-area-of-damage upgrade, doesn't really make sense to me.
Is the intention to encourage the player to aim only single-target at early game and transition later to area damage once they have enough health to tank it?
The player is really only rewarded once enemies are actually dead and drop the currency. But if the player is only dealing 1x attack damage while taking 3-6x the amount of health loss, it's more likely that they'll just die before getting rewarded, so there's no incentive to do area attacks in the first place. I don't understand why a player would move towards the area-increase upgrade, since you get nothing in return. If indeed there is going to be a late-game damage bonus for area attacks, it should outmatch that multiplication of health loss per click.
In this way, I think Nodebuster feels like it explores area-attacking more smoothly by having one of its first upgrades create a benefit, before doing anything like expanding the damage radius (something that is initially detrimental).