I wouldn't think it's collectors material just yet.

I have a GC8 with leather interior and wood grain steering wheel. They say only 250 were made (or about that number), but I wouldn't get any more dollars for it than a standard WRX in the same condition, mileage, etc.

For the Y2K plates, well the turn from 99 to 2000 was a bit of a fizzer. The Y2K bug never happened, nothing changed, so personally I wouldn't put any value on the plates if I was a buyer or a seller...