I've got a MIM Jazz i'm not happy with and to be honest just want to shift and get something else. I don't think it's worth dumping any money into them as you usually don't get much of that investment back if you sell it on.
Things I dislike with mine are unbalanced pickup output (loud G string and slightly farty neck pickup), plus it needs more defined sounding pickups, but i'm reluctant so spend any cash on it when it might still not be what I want (Jazzes may just not be for me).