Yoz, each person is different in how they travel, so putting a value on PS membership is hard.
First of all, QP single entry I'd place a total value of around $30 on. It's a nice place to sit and get some free drinks and food, but really it can be hit and miss, and every so often the main terminal has been the preferable place.
Additional FF points, again it's really hard to value them. It's possible to get a burn rate of up to 10c per point (my best effort), it's also possible to get a burn rate of 0.3c a point (my worst effort, I was points rich but cash poor and I really wanted to go on the trip)
Of course, there is always the brag factor which comes with having a PS card (which actually requires flying) over being an NB. (Contrary to belief on this forum, most ppl do not have status, so any status has bragging rights attached to it, esp among your non-status friends)
The one I think I would personally miss the most if I was to drop down to NB would be the free seat selection, the ability to select seats (it amazing how frequently a solo traveler can find shadows by selecting the right seats) is something I would miss on long hauls, and I probably wouldn't pay for the privilege.
Would I consider doing a status run if I was 20SC's away? Probably... Would I consider doing a status run if I was 50SC's away? Probably not, even if they came in under the value you had listed here.