Met timing requirements N/A?

Yes, you want to keep a pre-V10.1 version if you have many (or any) Classic Timing Analysis based designs that may still need work. At the same time, you want to start any new projects with TimeQuest on V10.0 (or even older versions), so you can migrate them to V10.1 easily if you need to. I believe Quartus 10.0 displays a warning, if you use the Classic Timing Analyzer, indicating you won't be able to migrate your project to future releases (i.e. you can migrate, but you will have to switch to TimeQuest for timing closure).