I'm a sucker for bouncy ball games and this is a good little prototype! I'd like to see an idle mechanic for causing the balls to bounce rather than needing to actively click. Maybe an upgrade could be for (a) pinball-style automatic plungers that activate every few seconds, or (b) launch pads that bounce whatever hits them and then have to recharge a while - either of these could go somewhere in the bottom of the level.

Could be nice to allow expansion of the level in some way, maybe so you could then buy upgrades like bumpers, repellers, extra-valuable walls... y'know, stuff to make more fun bouncy chaos :)