By all means add a spar. I was going to use a carbon arrow shaft for mine. This would be quick and easy. Here is a link to mine
http://www.rcgroups.com/forums/showthread.php?t=876488
Do a search on Sniper wing failure on RCGoups. I came up with alot. Its a very thin wing. It is very nice and flies well but it needs a spar
Jeff