To get good you will haveto go to somewhere else than renderosity. There is a lot I like about this site but it is not the best site for learning. You need to go whe  ethere are some top artists and see what they think of your work you need to go where you will get real constructive criticism.

   As far as tiem to make something I do think there are many that could benefit from spending more time on their work . But you have to finish, and I get to a point often where I feel I am polishing a turd. Indecision is one of the things that hold people back. If you get into your art go headlong into it. Have a clear vision of what you want to make. A lot of people spend a lot of time on scenes but a lot of that time is often wasted changing shaders changing the lights here and there moving object from one place to another. If you have a clear vision of what you want you will waste a lot less time on those things which can really eat up your time and make best use of your time.

The wit of a misplaced ex-patriot.
I cheated on my metaphysics exam by looking into the soul of the person next to me.