- I find your comments interesting actually because you bring up many great points.
I will say this in response to the main point you are bringing up: Ever since July of 2011 when I first joined Google Plus, I have added people to my circles based on 1) comments to my threads that are engaging 2) comments in other people's threads which I find engaging. Both cause me to go to profiles of people I would never normally come across and explore their world. I have forged many, many great online friendships this way with some truly awesome people (from all creative and non-creative fields). I have gone on multiple photowalks here in NYC where I have also met people from G+ in real life which caused me to find them on G+ afterwards and circle them. Additionally, I have also done a major HIRL (hangout in real life) with many people who use G+ primarily for hang outs where I met over two dozen people who I didn't know prior to meeting them at the HIRL but promptly went and circled them after having a great time with them over the course of quite a few days.
There are limitations to how much people can take in and give out and that is not something that G+ will be able to solve completely. It's one of the reasons that I don't add circles but I take quite a bit of time to find out about people organically (sometimes via circle lists admittedly where I go through and check out people's profiles and add one by one when I have the time) and the only way I am able to do that is via comments (on other people's threads or on my own). It's near impossible to keep up with the amount of people who add me on a daily basis. I don't want to throw out the numbers here but it exceeds 1k a day. In the beginning back in July, I actually used to check out every single person who added me and I would add them back if they had a filled out profile! That was a messy system and a system that doesn't work past a certain point. I have since refined my circles.
However, that brings up another interesting point. In my highly interactive circle, I have 120 people (I don't put more than 120 in each circle because it gets too overwhelming). I would wager that many people have circles they interact with more than others which includes the people who comment on the threads of those they have in those favored circles. If you think about it that way, everyone is bound to miss out on tons of people that way despite having circles they are highly engaged with where they find new people to connect with via those subsequent comment threads. I am not sure what the elegant solution is to this conundrum to be quite honest. That is the core issue though.
I know now by visiting your profile after reading your comment here that you obviously circled me at some point. If people comment on my posts or posts of those I interact with regularly here, I tend to eventually migrate over and add them to one of my interactive circles. However, based on the conundrum I typed out in the paragraph above, sometimes you do miss people...