I'm currently transforming my cubic 3x3x5 into a proportional one. I had it fully functioning and it only needed stickers but my friend had grabby hands and butterfingers and unfortunately dropped it from about 2 and a half feet and almost all the extensions broke off. I was using Krazy Glue (http://www.dickblick.com/products/insta ... or-change/)
I think the bonds for the edge extensions should be fine if they're not dropped again but I'm worried about the thin stalks for the corners.
Any tips?

I personally like to use Gorilla Glue or Loctite. They are in gel form so I find it easier to glue extensions on without the liquid glue drying too fast. Did you sand the faces of the pieces that you were gluing together first? That will make a big difference in adhesion .

If you are concerned about the corner stocks snapping you can reinforce them by cutting a piece off a paperclip that is close to the same length of stock. Slide the piece of paper clip in the corner stock opening and then add a drop or two of liquid crazy glue and it will add a lot of strength to your stocks (credit for this idea goes to cooldayr when he helped me with this idea for my MM-337 and MM-335). Hope this helps.

That helps a lot. I'm sure we have some gorilla glue around here somewhere. I do sand the faces before gluing. My concern for the stalks is that there is only a very small area that's in contact with the extension when they're glued together.