Is there any advantage to request a in-person interview over a Skype one? I have recently applied to a PhD position and have been invited for a Skype interview. I am thinking about proposing to have the interview in person instead.

The website states that "interviews will be conducted either in person or via Skype", so in person interviews are possible. I will also not ask for any compensation, since flights are very affordable and I can be hosted by a friend.

My reasons to ask an in person interview is to get a change of seeing the campus/offices and to maybe appear more motivated and invested in the position. 

How do you think such a request would be perceived? Would it be slightly appreciated or make me look like I am trying to hard? Or would it be completely indifferent?

Furthermore, are there substantial differences with regard to the interview itself? Would it be "easier" in person because it is easier to connect, or is it "harder" because you are subconsciously by everything you do before and after the interview?
From my experience going in person is the better choice:


They will see you as very motivated and you show that you really want
that position and you are not just doing a quick skype interview (and
on the same day 3 other ones)
Personal empathy can develop much better in person than via skype
Your explanations will be much clearer e.g. using a white board etc
to explain


So, if you have the possibility then go in person!