i've owned all the aks as well, and the sgl are great rifles. However, it makes little sense to buy one as a shooter right now, unless you have money to burn, and you want to shoot in style. They have become collector items with used sgl 21 fetching $1500, and folding stock sgl 31 now fetching $3k nib. Like Wade, i've sold most of my aks due to market demand, except for my 5.45s (vepr and sgl 31).
If you buy a sgl, and you want it to retain it's value, avoid serious modifications like barrel cutting, as they lose value on mods very quickly. Evan spending $300 on russian furniture, and not having the original furniture will only make the rifle worth less.
You can find 107fr here and there for around $1200 a pop, and they'll have the folding stock, instead of the fixed stock. People will argue they are higher quality than the sgl 21, however, I haven't found much of a difference between the two.
I have kept one 7.62 ak, and that is a romanian wasr 10/63. For $600 I found this ak can do anything my other ak's could do, however, the finish is crappy, but this ak it's not a collectors item, at least not yet. At this rate, it seems like all aks will become collectors items.