Gold should be spent on a few things, depending on your goals. Mission refreshes are good for getting more credits, which gives slightly more credits than strait conversion of Gold to credits and also provides season pass xp. You can buy Variants that you love the look of if your interested in a unique collection. Or you can buy certain bundles with Gold that will often give both credits and variants (and even Collector Tokens) if you want a mix of both styles! As an additional note, as of the Spotlight Cache update, Gold can no longer be received on the collection track. Free to play player's will only get gold from weekly mission milestones, reaching level 90 on the ranked ladder, or earning it in the Conquest shop. This means Gold is very difficult to acquire and should be used wisely. For a higher amount of monthly Gold, the season pass offers more in the upgrade track if you purchase the pass, and the weekend missions offer a Gold reward if you use the featured season pass card.