Pretty good idea! I have something kinda similar myself with these periodical events that makes the game harder. My game's style is kinda similar to yours.
The game looks very nice, sounds arae amazing. However, there is one thing that makes me kinda frustrated - the fishies. The ground is too close to the bottom of the screen, making it very difficult to dodge the fish in time - if they spawn directly below you, you pretty much lose 1 life.
Scaling up the arena by 2 times might make it a lot more managable. Still, very solid entry.
(tbh I think I should enlarge my arena as well xD)