We all know about Prospectors, when you have a lot of them they become very powerful for gewtting your nice Legendary crystals, but there's something no one knows and with no indicator of its variable, testing would take too much time:

Do Captains improve your crystal yield value?

Sadly the only way of knowing it would be testing for a lot of time, but doing that may lead you to lose some part or anything even high valuable, so my suggestion is to put an indicator just like the defense, damage and cargo hold ones, but for the extra crystal yield you're gonna get when mining. This would raise with prospectors, and most importantly, we'll know if Captains really improve the amount of crystals.