There has been quite a lot said in these forums about the inner aluminum skins being an essential part of the structural design of your AS. It is not recommened that you replace the aluminum panels with plywood. On the other hand it would seem that a lot of people have overlayed their aluminum skins with various things. Some have used a thin layer of aluminum to achieve the new CCD style for example.
If you want the wood look I would suggest a couple of possible approaches:
The 1/8" plywood would be a lot easier to use than 1/4" which I think someone in the forums mentioned using. Not only would it be a lot more flexible it would also be only half the weight which would be important. If I were going for 1/8" plywood I think I would use either rivits or maybe small flat-head screws along with some panel adhesive to hold it in place. I would then cover the screws/rivits (and the plywood joints) with some narrow wood trim - something like screen door molding which is about 3/8" by 5/8" or so. From what I saw in my AS when I took the inner skins off the rivit heads holding the skin on do not stick out all that much. I would try just running right over them and let the panel adhesive sort of bride the gap between the back of the wood and the surface of the aluminum. Alternatively you could perhaps use some foam or cork underlay of about 1/8" thickness between the aluminum and the wood.
Another more expensive option is to use what is called a pliable veneer. Check out the following website for more information and click on "Products" then "Pliable Veneers":
Pliable veneers generally have a thin single layer of wood with a flexible backing glued to them. The idea is that you laminate them to some other surface. I think they can be cut to size with scissors. How much more expensive? The website above quotes $56 per 4'x8' sheet of white ash (the cheapest type avaiable). I saw 1/8" birch plywood locally for something like $11 per 4'x8' sheet. There are lots of very exotic choices available in the pliable veneers.
The above website as well as the following offer aircraft grade plywood that is thinner than 1/8". I was suprised to discover that you can buy 3 ply plywood as thin as 1/64". A 5'x5' sheet of 1/16" 3 ply aircraft birch plywood is listed there for $79.
Now for the really cool but possibly even more expensive option - check out the following website:
These folks supply several types of veneer products. Some of these veneers have melamine, resin and paper layers. Prices for these products are per the square foot. I estimated that the inner skin of my 31' AS has maybe as much as 600 square feet of area. There would be some reduction for windows but there would be some increases for cabinet surfaces, etc. The so-called bubble free veneer in white birch is listed at $1.99 per square foot in 10+ 4x8 sheets. Actually that does not sound too bad at that. That would be about $64 per sheet. If I had to cover 600 square feet that would be about $1200 worth of material. The 1/8" plywood would be about $209 (for 19 sheets).
The bottom line - I might have to give the wood options a closer look myself.
I hope all this stuff helps.