It may be worth a call to DPS to ask what documents are acceptable for proof of citizenship before spending $600 on a certificate or $100+ on a passport (not sure how much it costs nowadays).
I think for those of us who were born out of the country, we have to show that we are either a citizen or legal resident. In my case, since I was born in a dead country I am used to have my citizenship questioned often... one time I even had to show my dad's birth certificate because the official I was dealing with had no idea what the Canal Zone was.
