TechyInAZ :
upgrade to 16gb later when you think you need it, maybe in 2-5years? will have dropped in price by then too.
DDR2 prices peaked at 3-4X the cost of DDR3 memory after DDR3 became the de-facto standard (when I built my current PC, 16GB new DDR2 cost $330 vs $90 for DDR3) before crashing back down to similar prices to DDR3.
I would not count on DDR4 making DDR3 cheaper; it will most likely become more expensive for a couple of years as most production shifts to DDR4 and companies that depend on DDR3 for long-term support devices gobble up most of the remaining DDR3 production.