Personally I fly with the wingtips on, You can fly with the wingtips off then cyno them on if you want to see the difference, they are not structural and I doubt if they improve anything flight wise. For me they aid in seeing the plane as I have them painted white and they stand out in contrast to my purple transparent main color. I would say they would do little to change the flight characteristics but leaving them off would save a bit of weight but I honestly don't think its worth the bother.
Another question guys, hows your upright elevators looking because mine rocks crazily, guess its that tapered leading edge coming into play, inverted elevators are stable.