I'd say that if your "stars" are actually drawn sprites that,fitting them onto a power of two tiled background may improve performance...but if your stars are just pixels created at one side then wrapped,that creating them,destroying them offscreen and re-creating them would be better for performance...
I certainly think with 400 objects and only average 35FPS there are probably a few more places you could make big improvements on performance...I currently have a project with average 1000 objects running at steady 60 FPS
Just to add particles are a no no if you want performance up....