At level 235 I'm getting over 27k per hit, leveling only costs 2350, and it hasn't gotten any harder. Starting around level 20 I was gaining a level every click - I think your scaling needs some fiddling with. By the time I quit I was pulling in eight or so levels per bubble click.
Without any penalty for inaction, the "correct" way to play seems to be to wait until bubbles are already overlapping and click there. That has zero risk, and with the explosive leveling starting around level 20 the whole enterprise starts feeling kind of safe and like success is a foregone conclusion.
It is impressive how quick you put it together - I think with half that time again spent refining it you'd have a real contender here.