Steve:

The balsa spars are just to hold the ribs in position while you skin the wings. The strength is in the sheeting, and it needs the strong ribs to hold its shape. It's an old Dave Platt trick, a lot of the planes he designed are made that way.

Don't be afraid of it, while it looks like it will be heavy you'll be surprised when you've finished it.

If you really want to, I suppose you could drop to 1/16" for the wing skins if you glass it, but I don't think it's either advisable or necessary.

Bill.