It depends on your feelings about seeing a unicorn. Mod secondary speed can get to the point where it is worth considering an arrow with the right primary.
If you are not hitting the cap, I would keep them to maybe upgrade later. At your level credits are going to be an issue, so they may end up getting sold later without upgrading.
Personally, I upgrade them and if I hit more than 2 upgrade on something other than speed, I sell it and cut my losses.
I have a few with 19 + speed, and I keep them for situational use or tanks, if the primary is good. 11-13 speed can be a lot to cut off a toon, but there are times it can be worth it.
I have also seen a +28 speed secondary arrow.... unicorns are real.
So no, just selling them is not always the best move, but at your level you should have bigger concerns and that is not going to be a primary focus.
