This is a bit intricate to explain, so I'll try my best:
How can I get the list of people I've emailed at some point using my gmail.com account that:
1 – have already added me in a circle in Google+
2 – and I haven't added back yet
I want only those I haven't added back yet and that I have emailed directly, not via a mailing list. Mailing lists are a bit tricky, I am interest in directly emailed to/from me.
By emailed I mean that I have their email address in the To or Cc fields for all my emails in my Sent folder. I don't want the ones that have emailed me and I haven't replied.
Best Answer
What you're asking is simply not possible by using the given UI of Gmail and Google+. This is very very specific what you're asking and possibly you're the first one that actually wants to do that.
If you really want to achieve your goal you must create your own utility that will have to use the Google+ API for the circles and Gmail APIs and Tools to retrieve your emails. Something that I wouldn't recommend even trying it.