Start with your budget and set a MAXIMUM amount.
First off your deck looks great. Let the "Jones" that you put your money toward paying of your mortgage and watch there face turn green with envy. Though that info isn't deck specific it's just as good ;-)
As mentioned a quick pressure wash and a finishing coat of your preference might resolve your desire to make it look better. That being said....
I like the look of black iron and wood/red wood/exotic wood/composite. Replace as much of the railing with black iron and your choice of material with what fits in your budget. Pressure wash and finish the rest as above.
If your raking in the money. Do up the whole thing with black iron and X material and hire a landscaper to do some work around the deck. Add a built in grill, stone always looks nice. Keep it native to your location, but your talking big bucks now. Those are some ideas. Hope this helps.