I beg to differ a bit with the negative rap on the foams. OK, maybe I am just a super design and pour guy, but I always use foams.
What I usually do is pour mine from Alumilite products. I make up some Alumilite White with microballons, a small amount, and I pour it into the mold and rotate the mold to distribute the material. This coats the inside of the mold and provides a very paintable surface. I then make up the foam and pour, allowing the extra to come out of the vents and pour holes. The key is to mix fast and pour faster.
The Alumifoam skins well and has the same density as a white cedar. This stuff is more difficult to pour without over expanding, but figure it will expand a little more then two and a little less then three times the original volume. This stuff is so tough that it is almost hammer proof. When using a silicone mold, I normally have a couple of plywood boards for the sides and I put a couple of clamps on it to help maintain dimensional stability.
The Alumilite 610 (6 pound density with 10X expansion) foam has about the same density as balsa and is about as tough when it comes to pull out of screws as balsa, but it is a bit more resistant to breaking. I use through wire construction in the mold when I pour with this material. This stuff extrudes out of the pour holes and vents when it is still pretty soft. I normally just hold my mold together with a few rubber bands. I use this stuff with the Alumilite White skin and so far even muskie have not destroyed it -- but one did shatter when it hit a rock cliff at high speed on a cast. LOL
I find that both of the Alumilite foams mentioned skin smooth. They clean up well with a little sandpaper and a bit of wood filler fills any imperfections. I also find that if I hit the material with 600 grit sandpaper, hit it with a little alcohol, then mist it with a rattle can of clear lacquer, any paint will stick to it. FYI, this is just what I do with wood lures that I seal first.
I cannot comment on other foams, these are the ones that I started out with. I tried the Alumilite 320 and found it to be far to soft for my use, but with an expansion of about 20 times, who knows what can be done with it.
I would not discount the foams for your uses; they are just different. With a little practice, you can make excellent lures from it. I have attached a picture of what I do with these foams, and for what it is worth, I think this is more then a simple spook, etc.....