I finished my Connie a few months ago. I ran into the exact same problem on the saucer top as you did. The solution which you discovered was to add more rings for support. No matter how I tried to mess with smoothing groups it would not fix it.
Now I ended up with a bit more rings than I wanted but overall the poly count on this model was not very high so it wasn't as big a deal as I thought at the time.
I included a viewport shot with my wireframe so you could see.
I came up with this design years ago. I haven't modeled in a long time. I got the itch to have a go at this one. It's not your typical design. I wanted to get away from the typical saucer shape and thin nacelle pylons, but have at the same time be instantly recognizable as a Star Fleet ship.
Not even sure where to start on this. I fleshed out the hull and parts where the impulse engines would go and the deflector dish, but beyond that it's just a very basic idea at this point.