The Happiness Project just seems like one of those "oh let me take a year off and write about the amazing (trite) revelations I luckily had" books. I'm very suspicious of it being compared to the likes of Eat, Pray, Love. I'm not getting the appeal here, so maybe I'm missing something. Why are you so keen to read this book with the club?
I agree that reading non fiction would be a great idea, but I don't personally have anything to recommend. It'd be nice to read something challenging so that we could get a good discussion going. Then again, I don't know if that would then limit the number of people participating, and we seem to have so few already.
As for The Goon Squad, I didn't like it quite as much as everyone else here. The one thing I absolutely did love was how Egan played with the structure. The vignettes didn't feel disjointed at all, which is surprising considering that some were probably first conceived as stand-alone stories. (Thanks Guileless for mentioning the copyright thing. Would have never thought to look myself.)
Otherwise, I felt the book was well... adequate might be the word I'm looking for? I felt like it followed through with its themes well enough but that's it, really. The only part I disliked was the ending. Was I the only person who found the last chapter rather obnoxious? I don't have my copy with me, but there was a particular section about certain words that were no longer used (I think freedom was one of them?) that I felt was particularly heavy-handed.
Don't want to sound completely negative so I will say that I'm glad I read it for the unique structure, and I'm glad everyone else found it more worthwhile.