LOL I wish you had asked about this 10 years ago, when I could still do some aerodynamics work. I'd be checking NACA profiles and all that good stuff for you, but there's no way I can do that now. I have to say, just from an initial look, I don't like the design either but for different reasons.
My main concern is lateral stability of the entire tailplane. It looks like it's overbuilt for the vertical stiffness but next to nothing laterally. I noticed that some builders put in bracing wires, not sure if the plans call for it, but you're going to need them. Unfortunately I don't know if the wing structure is strong enough to make any difference. I probably would also recommend against lightening the tubing though, that's a long bending moment for the structure. Definitely don't skin that ass end either if you don't have to, that's for sure, or you'll just increase the lateral loads as well as increasing suseptibility to side winds. I'd personally think about a triangular cross section with a smaller vertical height, but then that's a bit radical of a design change and essentially changes the whole layout of the aircraft.
Also be wary of you CG too. Start lightening areas of that aft structure too much, and you're going to get nose heavy. Don't let your weight reduction compromise the stability of the aircraft, nor its strength. If you REALLY want to go lighter, you may think about rectangular or I-beam type material in place of the 2x2 square, but don't reduce that lateral strength at all. And watch your CG every step of the way.
Don't even get me started on those foam core wings. I'd also suggest NOT channeling or carving out internally in the foam. I work with the stuff enough that I wouldn't trust its strength if you did so. Build them solid profile, or find a different material, you'll be surprised how much pressure that the skin will compress onto the ribs.
Lets not forget that you're flying an extremely light aircraft, not a performance aircraft. The only purpose is to get you up in the air safely and under control, and it looks like the design is fairly proven in that regard. If you're chasing anything else such as speed, maneuverability or any other performance factor.... you're looking at the wrong class of airplane.