Refactoring a City

Hi, beginner here. On my second City now and I am still learning. I got a big blob of City Sprawl (0.7k), and now considere reworking it, or resettle.

Is it viable, to start a new part of the city with proper design, and remove most of the old city step-by-step? Or rather resettle and start with a grand design from scratch?

Any experiences or recommodations?