I like the idea of spending platinum on something like an instance. How about a rather expensive expedition (maybe with a lockout timer) that you can pay to enter. It can be an existing zone, but with loot tables changed to suit the end game players in most part? I figure those are the ones that have the most plat to burn anyway. I'm thinking the zone/expedition loot tables can contain some, if not all the items that have been proposed by OP.
This is a good idea as well...Just make it so that no plat drops in the paid fpor zones....like halloween....HOLY CRAP make halloween event purchasable that will bleed a CRAP TON of plat from the server...maybe only good for 12 hours then have a 24 hour lockout or something....100,000,000 buy in for 12 hours