From my experience negotiating a payscale at the regional level (which is obviously much different than the negotiations happening at major carriers) I can say that as far as pay negotiations go the company doesn't care about things such as cost of living in their city vs the cost of living in the city of rival companies. To them, pay is a budget line item they have to justify to the CEO/Board/Shareholders. That's not to say that they don't figure in dynamics of the workplace market when deciding what to pay non-contract employees (for example paying below industry standard wages for staff at headquarters because you conveniently located your company in a smaller community where you happen to the biggest employer vs a bigger city with more opportunities).
Since, however, the company looks strictly at what their cost of labor is relative to their competition within contract work groups (and you had better believe the big wigs talk about this when they get together for industry meetings), it would behoove unions to share contract information amongst themselves and look at the same things the company is: what a dispatcher makes at company A vs at companies B, C, and D. We as a collective of work groups shouldn't factor in cost of living of our peers when fighting for a new labor agreement. Not only is it irrelevant when holding discussions with management (who don't care), it is potentially screwing yourself out of future earnings by saying "My cost of living is x% cheaper than my peers at Smisek Airlines so I shouldn't be trying for as much money as them" AND it does nothing but weaken the bargaining position of your counterparts at other airlines when their next contract comes up. Which, in turn, weakens your position again when your next contract comes up.
The only time the cost of living vs level of pay calculus needs to be done is when you, the individual, decides whether you want to accept a position at company A or if you would rather wait for an opportunity with company B.
Now, if you want to argue the importance and monetary value of Quality of Life items in a contract and how much money each of those items are worth, that is for each union to decide on its own. Personally, I don't think this is a place to argue that math since each company's operation is so different that there is no real way to compare apples to apples on that point. My thoughts on what the discussion should be are: A) #teamGetPaid and B) "we have this in our contract, do you have something similar" and if not then C) "have you guys considered this idea to get added in to your contract?".