Let me see if I understand you -- you say that you bought the car from the original owner without a title? How do you know he was the owner? Are you absolutely sure the car wasn't stolen? Titles protect the buyer in a couple ways -- you know the car is actually the property of the seller, and you know what the mileage is on the car (in many states). If you don't have the title, you should apply for a lost or stolen title immediately to make sure you are the proper owner of the car. An affidavit from the seller might be necessary depending on your state's laws.
As for the value of the car -- I'm trying to figure out if you're asking if the value of the car is reduced if you don't have a title or if the value is increased because you are only the second owner. A title won't prove you are only the second owner, but without the title, in my opinion, the car isn't worth anything -- i.e. I would never buy a car without a title in a state that titles old cars. On the other hand, if you had the title and could prove to me with other paperwork that you were the second owner and that the mileage on the ODO was original, the car would be worth a little more to me than one with an unknown past.