This is pretty well done! The lance getting bigger and slowing you down which in turn means purchasing speed upgrades is a neat mechanic. Also incentivizes getting coins quickly before you're too slow. It's a bit weird that the best strategy I found is to mostly move backwards and rotate the lance (seems counterintuitive).
Some minor issues: At some point the game lags heavily (around the 1,000,000 points mark) - probably from too many enemies being on screen. The More Spikes upgrade in the shop is not available anymore when you start a second run.