It would be difficult to give it an actual value.
I don't think it matters so much the site was "owned" by you than the authority of the site it's getting it's link from. The authority of the site you're getting your link from and how you're linked are determining factors in the signal Google receives for that link. The true authority of a site and the importance of the link depends on many many factors such as the age of the linking site, the age of the link itself, the relevancy of the content/site, social presence...and the list goes on. There are over 200 ranking signals Google uses. My point being is there is so much more involved than you just being the owner of the site or not.