Sam,
One thing that I do to get motivated is to pick one aspect of the process and decide to get really good at it. I'll take a look at some of the posts at, say, CGSociety, and try to learn something.

Honestly, and this isn't meant to be a knock, after looking thru part of your gallery I think you could make a big improvement if you were to study lighting. Poor lighting can make or break every image. It separates the "drop some content into a scene and hit Render" folks from the really proficient artists. And IMO, taking on a big challenge and making incremental success at it is hugely gratifying. And, with me at least, it usually leads to a whole lot of inspiration.