Hi,
As per my understanding, if you want revaluation of currency balances on some specific account, this account must contain currency balances, meaning that currency balance flag must be checked for this account.

Ledger flag should play no role in adding account to revaluation list, but for accounts used in AP/AR (or in general - for ledger accounts) revaluation should be temporary only - it should be reversed next day, as revaluation imppact typically is not stored in subledger - it is GL process.