I don't live in Manhattan, but visit once a month on average -- and I will see 3-5 shows each visit. Previews, after opening -- doesn't matter much to me -- it's more about timing.
Shows I'm excited about I will usually see within the first 2 months of performances. I get around to seeing most things, eventually. However, there are shows that I simply have no desire to see, and don't feel the need to do so.
As far as repeat performances, I find the more a show resonates with me in an emotional way, the better chance that I will choose to see it again. That being said, I often see shows more than once even that don't speak to me emotionallly:
1. for my children to see it
Next week I'll be seeing Newsies again (as will my daughter) so that my 11 year old son can see it. I'd just assume never see it again.
We'll also be seeing Peter and the Starcatcher (first time for both of them, my 2nd) I'm happy to see this again, but likely would not have if not for my kids -- but a good friend could have talked me into it too, without much prodding.
2. I'm a teacher, and my drama club plans a trip each year. THEY pick the shows to see, and sometimes I've already been.
If we're not having fun, then why are we doing it?
These are DISCUSSION boards, not mutual admiration boards. Discussion only occurs when we are willing to hear what others are thinking, regardless of whether it is alignment to our own thoughts.