I'd say it's a good idea to get enough familiarity with code to be able to distinguish between good and bad code, and to be able to have a rough idea of whether something is well architected.

Spreading vision is an important nontechnical skill for a founder. I see this as distinct from but related to networking, being able to convince talented people to work for below market because they earnestly believe in the vision is crucial at early stages.

As a technical person working on a startup, I personally would appreciate a partner with more familiarity with the regulatory aspects of starting a business: filing paperwork, basic accounting, taxes, etc.

I also wish I had better Excel chops to better analyze data coming in (signups, revenue, expenses, etc), but am too focused on more technical areas to devote time to learn it.

I'm sure there are other skills that I'm forgetting in the moment, but that's a few anyway.