It's not just childfree women in their 30s that lvoe teh show. My son, who will be 32 at the end of this month loves it too. It's a cute show. And he grew up watching the ABC Friday Night line up, Sabrina The Teenage Witch, Boy Meets World, you get he idea.
I think it's appeal lies in a few areas, like you said, the acting, but also, it's a throwback to familiarity without being cheesy or without having to watch reruns. Cory and Topanga grew up, just like you did and just like my son did and I think there's an appeal in seeing that reflected on screen. it's where nostalgia meets the current day and when it's done well, it's magic.