Very entertaining, if limited.
Needs more upgrades to buy. Maybe for every 10 enemies beaten, you get a new currency, usable on death, to add further upgrades? (permanent ones)
Allow vouchers to increment?
Add up to two more voucher spots?
Allow Incremental to reach higher levels?
Larger view?
I did manage to get to needing 300 points to upgrade though, so kinda maxxed out...