Also depends on how much you value J over Y. Airlines value it at 10x, hence the high J fares (and most profitable one). Vacation pax rarely value it at 2x (most people will not pay double the fare for J, in marketing studies -- this is of course different on FT). Upgrades are generally considered to be the best use of points, but that is from a frequent flyer perspective (part of the benefit is earning additional points and future status, but it sounds like those are of negligible value to you). From your description it sounds like you are better off to use the points for the free Y ticket (so your points save you AUD 1500 and if you are happy with that, so be it).