I tried to change some things in the main game, to have more "random fun". The main problem in my opinion is the horizontal velocity (which is only impacted by initial values, so a bad start is always a slow game and a bad score).
I added a small air drag (plane velocity is slowly decreased), and an horizontal velocity boost on good cloud. I also changed the way plane is controlled to avoid abusing on gravity scale (use of AddForce with appropriate constants). I created an other branch as it is not a really scheduled task, and I'm not sure if what I did satisfy everybody. So, please, test if you have some time, and if everybody is OK, I will adjust the distance goals and merge that on master.
Of course, feel free to change constants in PlanePhysics as mine are probably not perfect ;)