What's with the plastic vacuum lines!?! The hard plastic lines that crack everytime you touch them. I'm slowly replacing them with the standard rubber lines.

What is the advantage to the plastic lines?

 

They are actually hard nylon tubing, and I believe they last quite a bit longer than their rubber counterparts. You likely would have replaced rubber lines three times by now, instead of one set of the nylon lines in 20 years. They also resist the higher underhood temperatures longer than rubber, but it obviously has finally taken its toll by baking the tubing dry. You can replace them with either type.