Smarter?
I don't see how doing anything can make you smarter. Your IQ, or whatever it is that measures intelligence is based on genetics and can apparently be reduced by environmental influences.
So I suspect, I'm about as smart now as when I started building but I sure understand airplanes a whole lot better now than when I started. I understand the importance of the structures - the spars, the longerons, the monocoque skin structure and how W&B plays into it all. I know how the parts work together and how bell crank works and stuff like that. For me, it is one thing to read about it and learn, another to see it and understand a bit more, and yet another level of knowledge to assemble it, have to make adjustments (like aligning the flaps, ailerons, and wing tips) to make sure the plane flies straight. The FWF is a whole new area of learning.
13 years ago I bought a Cherokee and getting my PPL taught me something about systems. When I take the cowl off the Cherokee to change the oil, I can tell you I look at everything in there differently now than I did when I bought the plane. I am no more intelligent today than I was 13 years ago. I beer or a glass of wine really kills 100 brain cells, I'm a lot dumber now than then. But unequivocally, I am far more knowledgeable about everything on that Cherokee (even though I didn't build it) than I was when I bought it. Building the 9A taught me a whole lot (as did reading some of the posts on VAF)
In my estimation, book knowledge it wonderful and experience is just as wonderful but put the two together and the combination is simply awesome. It isn't just about building either. Fly every plane you can - they all can teach you something. I wish I could put my finger on it but somehow learning to fly the "slippery" 9 has taught me things I never encountered with the draggy Cherokee. I'm a better pilot in both planes.
In my opinion, the experience building the 9A has been worth the price of parts. Considering I should get most or all of it back when the time comes to sell it, is just icing on the cake.