I've stayed at BWI five times - three water view and two garden. I've never actually paid extra for a water view at BWI - we've either received a "luck of the draw" water view room when staying CL before they made boardwalk view a bookable category OR just received a complimentary surprise upgrade to water. I used to prefer water, but now I'm not sure.
Water: Boardwalk is lively and fun to watch. I like the music in the evenings and the sound of the boat horn. On the one occasion that the boardwalk partiers were out late, I was with a friend and attending a conference, so it was highly entertaining and not the least bit irritating. On a family trip, I may have felt differently. It's a nice view, but I'd rather save the $ to apply toward a better view on a non-Disney vacation.
Garden: Peaceful. Very serene. Great for race weekends when I need to get to sleep early. Great value because the view is quite nice for the price. When at Disney, my husband prefers a view that helps him to forget that he's at Disney. Garden view accomplishes that. Water view does not.
We do care about view, and we pay extra for a better view at some resorts - we pay for pool view at AKL (savannah once for the kids, but I still prefer pool.) We pay for courtyard view at WL. We pay for garden at BC and YC. But the standard views at BWI are usually nice enough that it's not worth the additional $ to upgrade. We feel the same about bay lake view at CR, standard at GF and standard at Poly - the basics are so good that we can't justify the $ for the upgrade.