Hey George!
Nice 3d meshes!
One thing I'm noticing in your work, is that you are doing the exercises by focusing on 1 tool at a time (like for instance on this last one, you went 100% smudge). That is in fact good for learning's sake, but try to do some work using all the tools you already know well.
I propose this, because each tool has a very distinct feel to it (ie: smudge is "plastic", selections are graphic, etc). If you only use 1 of the tools, there's a whole lot of contrast that you are leaving out. If you mix them, you can add alot of variety to an image, and thus make it more interesting.
If you still feel insecure about this, then continue doing what you are doing, which is good, but for each 5 pieces you do focusing on a tool, do an extra piece using most of the tools at your disposal (or all of them).
Hope that helps!