Measure before deciding. Use performance data, search data, accessibility testing, user behaviour, and business needs to understand the problem before choosing a solution.
Keep what works. Preserve content, URLs, integrations, and technical solutions that still work well instead of replacing them simply for the sake of change.
Rebuild when necessary. Start fresh when the requirements call for a new solution or when technical and structural limitations genuinely stand in the way, not simply because a newer technology stack is available.