RE: 2nd board?
My recommendation would be to build a two board quiver. There are several reasons for this.
The HS is basically a very good board for light winds. Keep it for that purpose.
The HS is designed for straight line blasting, and not much more. A second board like a small carve will add a totally new dimension to your sailing. Jibing, jumping, small tricks, light feel, a new world will open for you.
It does not make much sense to try to sell the HS111, you will get far less money than it is worth to you.
As you state you are a light and intermediate sailor I do think the C101 would be an ideal fit. It is fast enough, and easy enough to let you hone your skills (as it is quite different than the HS).