I only rinse my kite if it has a lot of sand or mud between canopy & underside of LE. That is
an often overlooked area of the kite and can be a sand catcher. If you leave it in there it can cause problems. If you do rinse it with a waterhose, make sure to let it dry completely- fresh water causes mold and mildew, but saltwater doesn't.
The reason for not washing your kites is the chlorine and other chemicals found in tap water. Chlorine will deteriorate the threads, eat away at the coating on canopy material, and fade the colors.
If you think its dirty, take it out in the water and give it a quick rubdown before you deflate.
If there's not a good place to roll it up, (mud or sugar sand) loosely roll in the water and dry it out when you get home.
I try to avoid rolling up my kites on the sand whenever possible and it helps keep them in great shape.
More gear maintenance tips here:http://kiteboardingtampabay.com/kiteboarding-self-rescue.html