Running tape from wing tip to wing tip does help add strength to the wing because it stops the wings from "flapping" and bending. I actually did this too my little foam RTF and it did help a bit. It also helps keep thing wing together if you crash (Packing Tape works well.)

About adding strength to the horz stab, just do the same thing, use some packing tape. You should not need any type of balsa wood. Keep in mind that theys are not very "high tech" planes and are not ment to be strong and durable but too actually crumble if they are crashed so that the electronics are not damaged and the foam is actually qutie cheap. Also they should be flown in VERY calm winds, because it is very light and slight gusts will blow it off course.