I don't think what you're doing is too much, necessarily. Its kind of the way our safety culture is going. When I learned to ride a bike there wasn't even such a thing as a helmet to wear. Now, my neice and nephew themselves wouldn't think of getting on their bikes without their helmets and even I usually wear one now, too. It won't necessarily come to pass but it wouldn't surprise me, either if, in 10 years, we all wear helmets for all flying as a matter of course.
I personally still don't wear a helmet in regular GA aircraft but there's certainly no reason not to. Just be prepared to take a bit of stick at the club for the next 10 years until the above mentioned takes place.
On the Alpha//hg-55 issue, I don't know the difference in performance and weight but the difference in price was about double when I was looking into them 7 years ago and the profile of the Alpha is enormous compared to the HGU-55. The sheer unnecessary size of the Alpha ruled it out for me as I couldn't get it into the cockpit of the Pitts. In fact, I don't have enough headroom for even the HGU-33 with the visor cover.
These people that say it's better not to wear a helmet because of the weight/momentum issues are missing the point. I'd rather have my helmeted head hit the panel a little harder than my bare one because it's still going to come out better. With the strap angles in the SuperCub, though, I think you may have a point about the weight difference between two helmets.
See if you can find a place to try them both out and talk to someone genuinely knowledgeable about them. Regardless of which one you go with, it's a significant investment so you want to get it right, obviously.
As for pushing the boundaries of the machine and yourself, I'm all for that, but it is definitely a case of small increments at a time. I did exactly the same thing in the SuperCub and later, a Taylorcraft. If you're doing it and think you need a helmet to protect yourself, you may want to look at how you're approaching that.
Good luck with whatever you decide and stay safe!
Pitts2112