The exercise component is key with the physio. Whiplash is really a sprain, so you technically haven't had whiplash for years. What you've likely got is tightening and/or weakening of muscles and ligaments in your neck and shoulder as a result of you not moving your neck properly when you did have whiplash (this is the same reason as when hospitals won't give you crutches for a sprained ankle, sprains need to be moved to heal properly). Fortunately this is the kind of thing that physio is really good for, as they'll strengthen the weak stuff and loosen the tight stuff.
A good osetopath is great, but sadly they're few and far between.
