Joists, posts, floorboards, railings can all be repaired. Your deck can be sanded, power washed and stained and look quite nice and be structurally sound.
Many times my clients have thought that their deck was totally shot because of loose fitting parts, graying wood, and a few rotted components. Upon hear the price of replacing their deck there is often sticker shock. But when they realize they can repair their old deck for about a third of the price or less they usually go for it.
All that cash they save can buy a lot of Starbucks!