There are a couple of benefits that reapplicants have. First, and most importantly, they can demonstrate to USNA that they can handle -- and excel at -- the plebe courses at a college level. Second, they have additional maturity in that they're a year older, have lived on their own for a year (in most cases), etc. That said, a good reapplicant won't trump an outstanding h.s. student.
As for the way WP handles it, I'm not sure that USNA gives you extra points b/c of the extra semester of college. USNA considers all college applicants together. There's no quota (of which I'm aware), but you're basically competing against others who are similarly situated. And, of course, you're competing against others for each of the MOC slates. '
Bottom line (as others have said), if you were close as a h.s. student AND improve your application during that extra year, you have a good shot. If you were very weak as a h.s. student and/or don't excel as a college student, the mere fact you're reapplying won't make much difference.