You have a way to change experience to gold, but there is nothing to buy credits using gold. My suggestion is:

ITEM MALL:

Item One: Credit Box - Cost 10 gold - opened gives player 9,000 credits.

Item Two: Credit Box - Cost 100 gold - opened gives player 100,000 credits.

The higher priced one should give more credits so that players will opt to purchase that box instead. I see many players who are high enough level for a ship but need thousands of credits to buy. Those of us who purchase gold would love to have a way to buy credits using gold.