I believe the Pentax kit lens II is the better design by all accounts, actually, with later versions being the same design, at least. For a kit lens, as good as a kit lens gets, really. Quite nice stopped down and in the middle of the range. Weight about negligible, bulk, more than I prefer to carry around just to have true wide-angle, but hey.
My attitude toward a good plastic lens is mostly that it's a good plastic lens. With my old Canons I carry a mix of the solid-as-a-tank metal SSC ones, which I really love, and the later ones which are lighter and usually somewhat more-compact. Toward the end of the FD line, they started making a lot of *very* plastickey ones which in fact did suck pretty badly, particularly for QC and often cause they'd make optical and performance compromises to produce something more consumer-friendly. I think there's a certain romance about the old metal, as well as the fact that the first plastic lenses out there did have a tendency to be the cheapest available.