I maxed out my tornado! I had a lot of fun with this one - great take on an incremental.
If you continue to tinker with it, I think you could continue to expand the upgrades and add more in the sky - if you wanted, the tornado could take over the galaxy! Just swap the visual level indicators for a level number so you don't have to add a spot for each level, and add more assets around the planes (hot air balloons? bigger planes? low-orbit satellites? balloons and birds?) to keep feeling that progression as you keep traveling and climbing up into space.
Lots of room to keep going here if you wanted - really enjoyed it!