If you have 2x 4GB DDR2 800MHz modules, then it has quite a good resale value, because it costs like R2000 new for the 2.
I had to buy a new Socket 775 motherboard for my colleague, because it was cheaper to buy one with DDR3 + 2x 4GB DDR3 1333MHz memory than trying to buy 2x 4GB DDR2 800MHz modules alone.
If it is 2x 2GB DDR2 800MHz modules, then you would still be able to get like R200 for it. DDR2 costs considerably more than DDR3.
The single 4GB DDR2 modules are insanely expensive at like R1k each.