A lot of homes built in the 1980s and 1990s leak pretty badly, particularly those in cooling dominated or temperate climates. So what's "typical" in your area might really be that leaky, but they don't have to stay that leaky.

As I commented in an earlier post, homes built in colder climates are usually built tighter, simply because it's so much less comfortable when leaking sub-20F or sub-0F air compared to 45F air that most people would have long-since chased down the sources of those drafts and plugged them.

Skylights are usually a big solar-gain issue. You're never standing right next to them the way you do with windows, so their effect on perceive MRT at human scale near the floor is smaller, since they're surrounded by a field of warmer ceiling. If the skylights are double-pane and reasonably air tight they're not on the high priority list. Only if they're on a south or west facing pitch and driving cooling loads crazy-high with excessive mid to late day solar gains would it be worth considering changing them out. If you're able to cool primarily via nighttime ventilation I'm guessing they're not really a problem.

It's clear that much of the '90 era construction around here was without regard to heating/cooling efficiency. The climate is obviously very mild, and energy was relatively cheap back then. I know several people with single pane, 2x4 wall, lots of sliding glass, and they just do what it takes to heat it. Cooling is less of an issue because of large shade trees.

The skylights are south and west. We definitely get solar gain through them, but that's easily fixed with some retractable shades (on order now). This was an unusually warm and long summer, and we barely needed any cooling. Guessing 12 hours of a/c time. If we had solar, we would have run a/c more, maybe double, but generally we just open the windows and enjoy an 80F interior.