Additional Swifts can temporarily be generated through referrals and confirming information. After enough initial users have signed up these bonuses will disappear and income generation will be the sole source of new Swifts.
Swifts have no direct connection to any form of currency and are not backed by anything. Swifts are only worth what other people are willing to pay for them. There is no guarantee about the strength of Swifts in relation to any other currency.