There is very little good reason to either expand or contract the monetary base. The actual value of gil is determined by what's available to purchase and how much gil each individual has.

In an economy where players each trade with one another gil should circulate fairly rapidly. However, this is determined more by Square-Enix who is entirely in charge of what is possibly available at any time.

Really, and some have touched on this but not entirely, what is actually bad is a fluctuating monetary base. And by both reducing or increasing the amount of gil in the system, you can cause serious problems.

Now, I know some will think that by introducing gil sinks, it will help to counter balance the issue of gil being introduced into the system. This, while seemingly logical, cannot address the issue itself. For one, someone mentioned that gil being created by the millions from vendors. Now, if we try to address this by introducing a gil sink somewhere else... the fact that people will vendor different and varying quantities of items over time and people will engage in whatever gil sink activities that are available to varying degrees, it will ensure that there can be NO balancing with regard to the flow of gil into and out of the economy. This type of 'balancing' can only lead to a multiplication of 'fixes' that never actually deal with the issue.

In short, the number of sources for gil to either enter or exit the economy must be VERY limited in number. I am sure the developers are fully capable of measuring the quantity of gil at any time, and thus are capable of measuring the change in gil over time. If they keep the source for gil entering the economy constant, meaning keep vendor prices and leve/quest rewards stable, they should be able to modify taxes on the wards themselves to ensure a non fluctuating monetary base.

Also, some silly things I read:

Someone mentioned that if an item blows up, gil is taken out of the system. This is just simply not true. There might be gil lost in the process of making and selling the item... guild synthesis buffs, or purchasing items from a vendor. But only items are destroyed. And the gil you used to purchase those items is safely in someone else's pouch.

Also, the fact that people have vary amounts of gil is directly related to the degree of time/effort and intelligence with which a player invests himself in the game. Larger quantities of gil usually can be extrapolated as meaning this person has spent more time or has spent their time effeciently while playing. And in general, most gil is rewarded to a player for doing a service, either gathering materials or crafting those materials for someone else. Someone who has made lots of gil and saves most of it is a pretty charitable fellow. Considering he does many services to others without asking for much in return. Such a fellow surely has a greater claim to the services of others. I see no reason why large amounts of gil are bad. Obviously those who earned their gil by vendoring items perform no service to others, and this is partially why I think vendoring items should be entirely removed from the game. But that's another topic.