If gold is going to be a little easier to obtain.
If items are going to cost more as a result.
This is basically inflation.
So logically speaking, existing gold in a player's account should be increased. If I have 10k gold stockpiled, I should at least get some equivalent amount added to this, to account for this inflation. Otherwise, you're basically forcing me to buy items, since people aren't going to be punished for having black armor already, even if they payed "less" for it.