this is great and you have very good art ^_

I think you should go the route of generating forests, it can make for something interesting even for the developer after creating something like that. To do this there are many ways, but the one I suggest is to create terrain and objects separated from each other, and the objects will all have some anchor point (such as tree the anchor will be an x,y near the bottom) this anchor point could then be used in generation to know how to place the trees/objects along the generated ground, and you could also do this same tactic on background for parallax effects, or use the anchor as center of rotation for greater variance. Parallax is important either way I think because a foreground tree or two along with some background trees all scrolling at different rates gives a sense of a much larger world, you know?

Anyway, I am just throwing out some things for you to think about, in the end I say just do whatever you find entertaining to work on and the game will have that shining through after you're done, people will notice this :)