Well, if you mitered the front piece and then sanded it to round, it would look real good. Someone on here has detailed the process in the project announcment forum.
As to the other one, you could use bondo or spackle to create a fillet there. Slop the bondo on the gap, then use something like a spoon, or other round scooper thing and drag it along the seam to create the rounded shape. Once you feathered the edges out, it would be a very smooth transition.