I believe that Attachment makes positive role models in a child's life. If a child has someone to look up to and to admire. A child has the image of want it means to be a succesful person. If a person has someone who cares about them the person will try to act like the person who cares about them so in life they will treat oyhers they way they want to be treated. They will want to love, just like they were loved.
I think a positive role model is a likely possible factor that could influence a child's type of attachment and well-being later in life. The child will try to emulate the qualities they think are admirable in the role model, such as confidence and kindness. With these traits the child can have better self esteem and be better socially adjusted, which contributes to the child's well-being. A positive role model would also influence secure attachment because the child would feel more comfortable.
I think it depends on your definition of "positive". I agree with you if you're talking about empathy, kindness, etc. However, "positive" could mean a parent who is hugely successful at a particular thing. If a child tries to emlate his/her parent too closely, this could create pressure and feelings of inadequacy if these standards are not met, and thus create a competitve parent/child base, not a secure one.