The $450 will garner you extra luggage allowance, one free QP pass, ability to select your seat, the possibility of being higher up the upgrade ladder, slightly better earn on points and 50 SCs closer to holding onto it. I guess it depends on how much actual travelling you'll be doing in the next 12 mths as to if it's worth it.
In the grand scheme of things, I only really got use out of the extra baggage allowance - never had an upgrade request granted in many years of flying and I did have QP membership, so the extra pass I actually gave away. I found QF Silver to be a bit "blah" - not much on offer (after being WP & SG for several years) when all is said and done, whereas my CX Silver offers me better bang for my buck, but to each his own.
If you feel you'll get the use out of being closer to retaining next year (or even better hitting gold) then go for it; it all depends on how much flying you'll be doing over the next 12 months as to whether that $450 is well spent. :mrgreen: