I've never been a fan of those hard cut-out lines, so maybe (and that's not critisism, but just a personal opinion :) a little softer lines by fading the images into eachother would make it a little more special ? Just don't get stuck in thoughts that people/objects should have be on there completely, cut out very precisely. I never use anything else than cloning one image into another (seperate layer) with a soft, large brush. It helps working on the images first (changing backgrounds, etc) before putting them into your final work. Also, more of an idea, try to bring back copies of layers you already used to let part run over front layers. Like for instance taking your bridge photo, and make certain objects (that logically should be at the front) fall behind certain elements of the bridge (which is the object that is far away). Or like letting one of the bridge's pillars run in front of the table, instead of behind it. But cloning instead of wasting hours on cutting stuff out would be an improvement generally to people's work without any doubt.