By "the AI seems to have gotten worse" I men't that more in the sense of "dumber", like they seem less 'aggressive' and aren't moving around walls to get to the player as much in addition to not making a straight line (Which is why I thought at first that the player was faster then the enemies), but that might just be me interpreting it as such.
I say it is reasonable to make it so the player can't survive infinitely. After all, this is a game where you are suppose to lose after a certain point. There could still be progression in the game without changing the gameplay to , where after you get a certain number of points you are allowed to progress after you finish your game where you are while still able to try and get a high score where you're at.
And a few random ideas here: each time you collect a recharge power up it because less effective, recharge and spawn time get reduced to 1 second to increase intensity along with spawn time for coins, everything has increased speed (progressively or originally), if you are going to have a level system you could have a ghost level, different types of coins that could give you more or less that are RNG based though have rarities (I.E: "blue coins" give you 20 but are slightly less commen then gold, silver gives you 5 and are also slightly less common then gold, reds are worth 50 and are even rarer ect), change the sound effect for when you click on something (it sounds like a tight fart and it's a little annoying), boss level (after you have already developed a progression system).
That's all I got for now, not sure if any if this feedback is useful but I hope it helps.