If you're scarfing and laminating you could probably put a lighter piece of wood in the middle to more nearly match the properties of the spruce, though you'd have to think about loads and orientation carefully first.
Although I'm not sure an open source airplane is feasible, I think some of the issues kicked around here are interesting.
One goal might be something like a VP-2 but enclosed. It may be that some of the newer materials, not necessarily the ones we think of as high tech, might enable something that hasn't been done before.
It ought to be possible to make an airplane that will fly quite well on only, say, 30 or 40 hp. Probably needs a long wing. Those Briggs engines can probably be fiddled with to get some good results. I recently saw a page someplace where they're selling 35 and 40hp (originally in the 20's) Briggs converted with PSRU's, etc. About 4k in Euros, but I don't know the conversion rate these days. The French Luciole uses a similar engine. I suppose the more reputable VW engines are the other viable alternative, as long as they're not pushed too hard.
I think another barrier, besides cost, for people is the amount of labor required to build a plane. Anything that can simplify that and still get good results is probably helpful. On the other hand, by now maybe everyone has watched so much TV that they won't go for anything that's not cool and sexy.
Using wood probably requires a skill that needs to be carefully developed before one picks out something for an airplane. I think there IS some nice wood available occasionally, though it's hard to find. I saw some Port Orford Cedar not so long ago that looked very nice.