Does seeing a person's vulnerabilities make them more lovable?

Sometimes. I think it gives you insight to their personality that you would otherwise not see. Watching someone deal with hardship can be endearing, especially if you already care for the person.

However if all they do is show vulnerability, they may come across as weak. I think their ability to express it and manage it is what makes them lovable to me. People who aren't afraid to show their soft underbelly is something that often takes courage. I can respect that in a person. But I have a hard time respecting people who expect to gain sympathy from always showing weakness.

Or easier to manipulate

My best friend is a huge (as in he's really big) football jock. He's the epitome of someone you are not to fuck with. He's strong, funny, and charismatic. I love all that, but I love him most when he talks about his ambitions and his uncertainties about the future (his vulnerabilities). He gives me opportunities to support him, and this reinforces our bond.

seeing a persons vulnerabilities makes them more able to be screwed over....

That just depends on their vulnerabilities... As a rule though, yes it does!

Females yes. Males no.

yes it does in the sense that it makes you feel more of compassion which is a type of love, well that's how i feel anyways.

It depends who and the type of vulnerability.

In a way, but constantly whining about things begins to grate on the nerves rather than invoke any sense of empathy after a while.

When people purposely show their vulnerability and do it often just to get some sympathy, it's annoying. This makes them seem weak to me. Those kind of people generally do this in publicly in front of groups of people. They are attention seekers and desperate.
As for people who are generally not so quick to open their selves up and display their emotions to you, it can definitely make the bond grow stronger.

Yeah, if you open up to someone, they start to like you.

Just don't pour out your heart to everyone you know, because that's plain freaky.

I think it can make you love 'em or hate 'em. When I see a persons vulnerabilities I definitely see them differently, but not always in a good way. I think that's why I find it difficult to get close to people. But there are a select few whose weaknesses exalt them in my eyes.

I hope not because I rarely show weakness.