Making them heavier isn't going to make up for the fact that they're coming off nock low, which is just what you DON'T want. You can get away with quite a bit of nock high on a target rig but nock low isn't good. I think you're going to be better off sticking with what you have and improving your form and technique than you are going to be throwing expensive band-aids at the problem. Save the money from new arrows and sights and bows and spend it on a good coach, if you can find one.