There are few certainties in life. You definitely can't guarantee that doing an internship will boost your pay if you were to go into GP. It might, but it many cases it may not. There are so many more factors that go into choosing a residency candidate than only their experience. I do believe that in the vast majority of instances, yes, a program will likely go with the internship-trained veterinarian over someone who did "just" a year in private practice. But who you know, who is writing you letter of recommendation, how strong those letters are, and how well people think you will mesh with their existing group are also very important factors and in theory if the non-internship grad is the best candidate, they may take them. But in reality, most residencies are insanely competitive and, like Hyge said, it seems unlikely. Maybe not impossible, but unlikely. Heck, for many specialties, people have to do TWO internships before snagging a residency. There is also a sense of 'paying your dues', be it right or wrong, surrounding the internship/residency process.