Hi Art.
I really relate to this post, both on the origin of the feelings (childhood abuse) and the coping strategies and "resolution" in response to it in the long run. In my experience, this issue did not go away at all and repeated itself in a variety of forms until I truly faced and processed it. I actually think some of the effects and consequences probably never go away, but once we deal with it appropriately, it gets placed in a "past compartment" and does not influence our choices and behavior in the present in the same way. I would really recommend to you to find some safe way to process your feelings, which probably best to include talking about them to someone. And of course a lot of honest introspection and exercise in self-acceptance.
The volunteering is a great idea if you are inclined to do it. I think what you mentioned about finding an area where you can "project" your need for feeling significant, useful, and accomplished is a great way, too. I personally found this in my profession, but I did have a problem in the past over-identifying with it (with my professional role). It was hard to drop the maladaptive part without harming the constructive part, but I will say it's feasible. I also recently found a good source of this from participating here on SR, which has been quite a discovery for me because I did not see myself as a helper kind of person before, and I feel it's very rewarding.
I think finding and doing something you are genuinely passionate about and which suits your personality is the way to go in terms of getting this feeling of significance. I did not have problems finding such a "niche" early in my life, but I then had problems due to my perfectionism and fear of failure related to it, which I only addressed quite recently. I will also say that carving out a unique way of contribution to something I feel passionate about amplifies the feeling of accomplishment.
As for the original events that triggered the emotional pattern, again, I definitely suggest that you talk to someone about it.