Cool, it's not actually a problem that I couldn't tell what those couple of things in your scene were by the way, I think it adds to the kind of ethereal nature of the scene, which is good. Fair point on the volcano, the way i was suggesting it was to have it way back in the distance anyway so again you could've faked the smoke with a texture plane. However, as you say you're not in to the texturing side of things then fair enough if you don't think you'll be able to incorporate that or the mountain planes (With the mountains by the way you wouldn't actually have to texture them, just create mountain shaped planes and cover them in fog so they become silouettes in the backdrop, no texture required, not saying you should do that, just pointing out a way you could cheat for future reference)
The meteorite thing is worth trying, if one of the meteors had landed in the foreground and was larger than the ones in the sky it would help with the sense of scale, making it seem like the ones in the sky were further away.
Worth trying, but what I always do is save a few copies of these sort of scenes and try different things out on each, then if they don't work you have your original to fall back on. I wouldn't want to go ahead and suggest you should definately add something that might mess up your scene