I dont think they will become a collectable like the earlier GT's, but with the limited numbers around, I think they are a bit sought after even now by people.
People who know just how sweet a ride and good overall package, and as time goes by and the attrician rate takes more away they will become more sought.
As said above, there was only around 350 S3 manual XR8's and 950 auto S3 XR8's made, and how many of those now are left?
I know theres also a decent number that no longer have their complete Rebel body kits either because they dont make them anymore and every hit in the back usually spells the end of that part.. Once thats gone, the cars then missing a part of its uniqueness IMHO.
Id say price wise, they have bottomed out, that price will fluctuate somewhat with the quality of the example for sale, but I dont see em going less than they are now.. Their a lotta car for the $$ thats for sure.
To the
OP, Id keep it and continue to enjoy it, no point in selling it and theres nothing better in the later models Falcs unless you wanna spend GT money.