I think the short answer is this. If you are going into a procedurally oriented advanced program, then yes, a prelim surgery program might be a good learning opportunity. You will put in lines, get very adept at suturing up oozing wounds, get comfortable with post procedural complications, and learn a lot of anatomy from the inside out. HOWEVER it tends to be a very tough year, where you will be working 80 hours a week almost every week, with minimal elective time, lots of ICU, and thus if you can snag a transitional year or cushy prelim medicine year, you do. Programs range from very benign to very malignant, with variable opportunity for prelims to see the OR, so you need to get the word of mouth. But if you ended up with an advanced program and no prelim, it's certainly a lot better than derailing your career.
Now for everyone else a prelim surgery spot is a bit dangerous, as it's often a dead end. I know a couple of people who turned prelim spots into categorical, but they worked exceptional hard, and several others in their years didn't have the same results, ended up wasting a year. For foreign IMGs with inadequate US clinical exposure, I would think a prelim surgery year should satisfy most critics, but haven't met many people who were successful on this route.