I understand what you mean about chapter sisters a bit. I don't visit my chapter at all, at least since I moved away from it. They aren't the best at alum stuff, and besides having rush connections who give me info on that, I unfortunately have nothing to do with them. So not exactly the same situation, but a bit similar.
I really think that alum stuff is what you make of it. If the alum events don't work for your schedule, contact someone and try to work out an event that will. You could plan a happy hour, a dinner get together, that type of thing is really easy to host. If they types of events don't work (like they are all "date" events and you're single), let them know. I really wish members in Boston would let me know events they want, I have no idea how to get them to come to things. So I just plan stuff that I am interested in and hope for the best. I LOVE to hear from people.
When I first graduated, I started the position of Collegiate Liaison for my AC because they didn't have one. Now I'm trying to start up a Mom and Tots group because I want to find sisters with kids. Maybe consider what you'd like to do, and get involved! There is a small chance that I may be moving (but I haven't told anyone that yet, so don't tell my region!), and I'm already thinking about how I can fit myself into this group which seems very different from me. Maybe contact the AC and ask how you can contribute? Is there a collegiate chapter near by that you could volunteer at? There are ways to do that besides holding a big adviser position if that's too much for your schedule. Or ask to be on a committee on the AC. I'm sure they could always use volunteers.
What school was Theta Delta? Also, I think it's great that you are contributing as you are. Not enough sisters understand the importance of that, and I think that any group would be lucky to have you involved as you are obviously a dedicated sister. I'm probably not helping much, but I wish you luck!