I've been doing some looking at the literature about game economies and the necessity of gold sinks and how they should be structured. I haven't seen anything that indicates that gold sinks need to be universal in order to function properly. Gold sinks exist to remove credits from the game economy. As far as I've seen, whether the gold sink is "universal" or will only impact those with excess credits to burn doesn't seem to matter.
Have you found any sources that would indicate a gold sink needs to be universal in order to work?
I've not looked for any sources that claim a credit sink should be universal, nor do I have to find any to make an observation on already evident facts. I recall simply pointing out that the proposed alternate credit sinks are not universal while repair costs are.
Repair costs are not voluntary, while the proposed alternate credit sinks would be. Do I have to go find a source that claims that credit should not be universal to make that observation?