You have a good handle on the pros and cons of each school. It’s tough for any school to beat the in-state cost for Cal Poly, so you will have to decide if Lehigh is worth the extra expense. Some other considerations:
As a college town, San Luis Obispo is livelier and more attractive than South Bethlehem. The catch is that SLO is all you get; it’s a long way to any major city. Lehigh is within bus distance of Philadelphia and NYC. If you wanted to catch an exhibition at the Met, for example, you could leave South Bethlehem on a Saturday morning, be at the Met in three hours by bus/subway, spend the day in Manhattan, and get back in the evening. Not saying that Lehigh students go to the City every weekend, but they do sometimes.
Neither of these schools is noted for high minority enrollment. However, the campus minority communities will be numerically much larger at Cal Poly, simply because Cal Poly is a much larger school overall (~20,000 undergrads vs. ~5,000 undergrads). One exception is that Lehigh has more international students (8% at Lehigh, only 1% at Cal Poly, according to College Navigator).
Cal Poly’s enrollment will consist overwhelmingly (83%) of other Californians. Lehigh has a broader reputation, and their students are more likely to come from around the country or internationally, although the largest concentration (about 60%) are from PA, NJ, or NY.
Cal Poly is a “polytechnic” school that emphasizes “practical” fields like engineering, agriculture, and business. PoliSci is in the College of Liberal Arts, which is only about 15% of the total enrollment; this could make you feel like an “academic minority”. Lehigh is evenly balanced between the Colleges of Arts & Sciences, Business, and Engineering, with a lot of interdisciplinary study between the colleges. Many A&S students get a second qualification (double-major or minor) from the business school.
Cal Poly has strong job placement in California, including both the Bay Area and Greater LA. Lehigh has strong job placement into the Boston-NYC-Philly-DC urban metropolis. So one could be better than the other, if you had a geographic preference for life after graduation.