Interview at third-choice University - what to do

N

Hi and thank you for your time,
I've applied to four universities to study my PhD and the status of my applications is:
1st choice: as I explained in another topic I got the unofficial acceptance confirmation of the department and they have forwarded my application to the Registry.
2nd choice: last Saturday I got an official admission offer.
3rd choice: just received a mail inviting me to an interview in 3 weeks.
My question is if you think that I should attend this interview. There are several reasons for not attending:
-It seems not to be so good as the 1st and 2nd universities. In fact I included universities 3 and 4 because, being an international student, I didn't know which my chances were, and decided to apply to 2 highly ranked institutions and another 2 as "backup".
-I already got an offer at my second and (hopefully!) first choice.
-I live in Germany and I would have to book holidays, buy a ticket, arrange for accomodation...
But I'm terrified about the possibility that the other 2 universities change their minds and don't accept me!
What would you do? Would you attend or not?

4420