Yes, I cover bare balsa with silkspan. I get medium weight silkspan from a place called Easy Built Models. It is the real stuff, just like we used to get years ago.
Here is the way I do it, but there are other methods that will work: I apply clear dope, maybe two coats, to the bare wood. Sand lightly. Dampen the silkspan and apply dope thru the wet silkspan. After this dries, I will apply two more coats of clear, then sand.
As far as the ridges go, it is better to tear the silkspan, leaving a somewhat ragged edge. After several coats of dope and sanding, this edge will disappear. Do the same with the overlapping piece and you will hide that edge pretty well. A cut edge, as you discovered, is harder to hide.
I see no advantage to using polyspan over bare wood.