Have paid and used it several times, in your case, for that distance flown, so long as the plane is a 737, and won't get swapped to a 320 or an F100, its good, esp if you can pick rows 3 - 6/7, as these do not have the quasi "over wing exit help them" talk, I am ashamed to sit in the over wing exit zone, as you have to watch the crew telling you their scrip.
$50 per sector is not all that much, seeing you would have paid $199 for the trip, prior to economy X fee.
You can also buy lounge access in Aust at the VA the Lounge domestic reception counter, ...
Economy X does not give extra or more SC, and you get the same type of food as in Y, except you have a bit more overhead bag room, more space in front, greater chance of a shadow (depends on loadings of course, time or day, day of week, school hols or not).
I certainly would do it again.
If your plane is a 320, then its only row 1s , and over wing economy X, or it F100, also over wing economy X, for which you will get the spiel with the card on seat.