If you sheet the spi too tight the leech curve becomes too large and will flutter no matter what you do, at least this is my experience. There is a reason you dont see large roaches on jibs, unless you count the AC boats with leech battens on their jibs..
Usually leech flutter is a sign of a spi sheeted too hard or a stretched leech. It is common that both leech and luff lines are installed, but they would be easy to install by yourself if you need them.

You wrote that you was trying to point. Going upwind? You can go quite hight with a spi, but you must flatten it by letting out on the tack or the halyard. Leech will flutter, but in weak winds it might be worth it if you are not going to A mark but are distance racing.

I find spi telltales very valuable on the Tornado. The luff curl is good, but the telltales are right in your face when going downhill. Funny that the olympic Tornado teams dont remove those attention grabbers from their spis <img src="http://www.catsailor.com/forums/images/graemlins/smile.gif" alt="" />
We trim the mainsheet in medium winds, but in strong winds we use the main traveller and steering.