One of the attractions of the RN game is that there are different styles of play open to the players. They can play in different ways over time, keeping interest high. Workers strangely are an area where there is some balance. Clearly a city team needs to be a strong one to compete but if it has 25 good members there is no reason why they cannot compete for any workers. Additionally the goods based workers are usually only of interest to the city haulers.
The practice of closing an association & reforming is used by smaller free hauling teams to get cheap workers and it is effective if the team is small but in so doing the players are opting out of the association competition so this affects personal rank only.
The number of players is what makes playing style work - in a relatively lightly used server then free hauling is very effective. How often does free hauling do well on a really busy server where a majority of cities are active?
If the aim is to eliminate closing & reforming then a penalty could be imposed on those that do this - losing pp for instance of delaying for several days before they can get workers (might be hard to program though i guess). Small associations playing normally should not be penalised though in the manner suggested - they are in the lower ranks due to being small & have fewer p[layers to contribute so it is fair that they have cheaper workers overall to my mind. If a full 25 player association pays 25 mill then the equivalent for a lower ranked 4 player association is 4 mill. That is paying the same per player.