Yep, I would never bother buying points, unless it's purely because you need a few extras to complete a redemption.Once you factor in the charges/taxes/fees it's probably closer to $6500 to $7000 at which point you could actually look at cash fares probably (not SQ but others like China Eastern etc or Vietnam airlines)
So you BUY all those points, then have to pay all the charges, taxes and fees on top AND don't earn a single point or status credit on what is effectively a cash fare, but not treated as one.