When I have studied this passage, I tend to think that it's more about the conversion (or re-thinking) of Peter and the circumcised than of Cornelius and the Gentiles. (See also change that was required of Jewish disciples in Acts 9:26-30.)
Similarly, the first account of Saul's conversion also becomes a story about changes that needed to take place in Ananias (Acts 9:10-18).
It forces us to look at ourselves (and our congregations) and our views towards those outside the church, and those we might consider "unclean".
There's no limit to whom God can bring into his family.