But are you rebalancing here? The rich players who have saved huge amount event resources from previous events already have all the "cool items", otherwise they would have used the leftover event resources to get more cool items.
Also, even if there was another way to gaining the tokens to newer players, the rich players would still have a huge advantage.
Now, I understand that this is a way to compensate these players, and by allowing the resource conversions, you are already doing this. The only thing that you will be "robbing" them is the opportunity to get obscene amount of resources through trade (assuming they already had what they wanted from previous events), thus making the rich - richer.
This is your decision to make. but I have to say it's a little disappointing.