I think the key going forward is to make a lower-budget Doctor Who. This doesn’t mean doing what they’ve been doing for the last few years, but with worse effects. Rather, a fundamental shift in how episodes are constructed. We don’t need skies full of spaceships and continuous world-ending stakes; Doctor Who was never about spectacle. Instead, tell smaller stories with scaled-back settings and limited characters. But more importantly, focus on character, atmosphere and tension.
There definitely needs to be a push to add more enemies to the roster. The fact that they brought back the Rani really felt like they were scraping the bottom of the barrel for villains to bring back. But as with all things, there needs to be balance. There’s no harm in bringing back a few old favourites; there is a reason that they resonated in the first place. Just make sure there is a story to tell and remember that even if they’ve appeared before, there will be some in the audience experiencing them for the first time. And your exposition must be better than stopping the plot dead so characters can watch the old episode!