Well, perhaps i didn't describe our (admittedly off-the-cuff) testing very well. We jacked up the extreme corner of each car--not at the jacking points on the sides. We jacked them three feet in the air in fact. Certainly the car can support its own weight, but the amount of torsional force we were applying certainly went outside of the realm of what the car was designed for.
However, this was on a coupe, and so I'll defer to you on this one. I agree that putting strut tower bars on the boxster would help give a bit of a "lid" to the "shoebox", so to speak, but i'm still hesitant to say how much it would help. Again, why no option for this sort of thing from Porsche themselves?
I've seen it time and time again where people want to believe a modification helped them when in reality it just gave them confidence to exceed their personal limits. I'm not saying that you're full of it or anything, just that without formal testing I am always very hesitant to accept any sort of car modifications.
In spite of all of this talk, I DO have front and rear strut tower bars on my Eclipse.
I just don't put much faith in them. The fact that they cost me less than $200 together and are about as solid as they can possibly be makes me not worry about it too much. Of course, next to the $4000 or so I spent on suspension tuning and R&D, one could say that the benefits of the strut tower bars could be masked--hard to say. I haven't been all that scientific in my testing either, I suppose.
I've been considering a front stut tower bar for the 987 and that racing dynamics one seems like a valid candidate, but geez, it's $300!
I have just the right turn to test it out on too, much like you do...