These aliens are exposed to space radiation and they could potentially harm us unintentionally even if they are friendly. If anyone want to risk their lives to be infected by unknown factors such as chemical substances, radiation, diseases etc, that person certainly isn't me.

It's not logical to assume that mastering space travel makes a species ultra-advanced just because we think of it as a point farther down an imaginary scale of human progress than we're at. There are all sorts of ways in which it could be much easier for an alien than us without them needing to be super-advanced. They could be physically capable of surviving in space better than us, or live much longer, or have a biological self-propulsion system built-n, or completely avoided many of the scientific traps that have set humankind's developments back hundreds of years, or simply have figured out one little thing we've missed that makes all the difference.