Lol glad to know I'm not the only wierdo, as I too have thought about it in passing!! I think yours would be easier to accomplish it with as the 91-92's have the similar rear wheel openings to the wagons..
If I was to attempt it, I would do it with a painting system rather than a decal that would peel/lift eventually..
Jdee and the group over at Grain-It Technologies are pretty friendly. http://woodgraining.com
They have some nice stuff, that would not only allow you to do the outside, match your interior, but you could as make up some of the kit's cost by graining for other people!!!
When I have the money I would like to buy some of their stuff to do afew ideas I have kicking around!!
I have not seen a woody sedan. Sounds like a cool idea though, it would definately be different! I also think that the paint on graphics would be the way to do it. Step up to the plate - someone needs to be the first