Hi Julie,
I think your idea is fine. However, you do have to consider the grade. I am assuming you step down from your house onto the existing porch. If you cover it with decking, the elevation at the landing will be higher. If, for example, you now step down six inches, it now might only be two inches. I am just saying that you have to check this out to make sure it will work.
You might be better off just removing the stoop and starting over again.
Another idea is to re-surface the existing stoop with another kind of paving material, like bluestone. Again, the porch height will be raised now. The railings could be removed, and new railings installed. For this scenario, the porch itself has to be in good condition. The steps and risers could be re-faced also, perhaps with a beautiful face stone.
This all has to be looked at by a qualified contractor to see what can and cannot be done.
Add some pretty plants along the porch to give it a finished look, regardless of which way you go.
