I don’t have a micro architecture background so I apologize if this is obvious — What do power and speed mean in this context?

Power - how many Watts does it need? Speed - how quickly can it perform operations?

You can get low power with a simple design at a low clock. This definitely will not help achieve high performance later.

Clock rate isn't the only factor. A design can be power hungry at a low clock rate if designed badly, and if it it is... you're never getting that think running fast.

One could say "Optimize for efficiency first, then performance".