Make the platinum tokens how they are in osrs ; 1k coins for 1 platinum token.

For the rares just add a shop. Add the item "random partyhat box, random halloween mask box, and a regular santa hat" (similar to corp box etc.) Certain partyhats are rarer than others same with hween.
To buy this box all you have to do is exchange a certain amount of platinum tokens e.g. 500k (500m coins), 1m (1B coins), 5m (5B coins), 10m (10B coins) etc. This way you can sink the cash in-game and add rares too. You can decide the price of the box, it depends on how much and how fast you want the cash to sink in-game.

Don't add the black rares, rainbow partyhat and inverted santa hat to this shop or else it would ruin the whole concept of clan wars tournament, voting, pk raffle.

If this gets added i may play again.