You can either spend points or you can spend cash. There is not a fixed value for what a point is worth but 1.3 cents seems to be a good average of late. If you want to know the point value for a specific itinerary divide out the cents to buy it by the number of points to buy the same thing. In the example you've provided a point would be worth 1.36 cents, not 1.3 cents, as it is 43,500 point for $591 in value (I removed the $5.60 from the revenue fare, too, as you pay that in cash either way).

If you believe that 1.3 cents is a good go/no-go point for making a decision then simply divide the revenue price by the number of points. If the resulting number is higher than 1.3 then you got a good deal with points. If it is lower then probably not.

And, yes, if you believe the 1.3 cents number then you are "saving" ~$25 dollars paying with points in that scenario, but also giving up the opportunity cost of earning 9 points per dollar (Mint bonus and online bonus) so ~5200 points (or more if Mosaic or using the B6 CC). That's about $65 in opportunity cost.